[
  {
    "id": "italian-game",
    "name": "Italian Game",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/2b1p3/2BPP3/2P2N2/PP3PPP/RNBQK2R b KQkq - 0 5",
    "idea": "Fast development toward f7, then a central d4 break.",
    "structure": "Open center with active bishops",
    "plan": "Develop, castle, prepare d4, and attack only after the center is ready.",
    "whyLearn": "Italian Game gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Moving the same bishop repeatedly before castling."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4. This activates a bishop on a diagonal that supports the opening's central plan. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bc5. This activates a bishop on a diagonal that supports the opening's central plan. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "c3",
        "color": "white",
        "role": "player",
        "explanation": "White plays c3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Italian Game, connect it to the main idea: fast development toward f7, then a central d4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "italian-game-branch-1",
        "opponentMove": "1...Nf6",
        "answer": "e5",
        "explanation": "e5 gains space and drives the knight before continuing development. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Italian Game video lesson"
    }
  },
  {
    "id": "london-system",
    "name": "London System",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbq1rk1/ppp2ppp/3bpn2/3p4/3P4/3BPNB1/PPP2PPP/RN1QK2R b KQ - 4 6",
    "idea": "A repeatable development shell with a safe king and a timed e4 break.",
    "structure": "Closed center with a sturdy dark-squared bishop",
    "plan": "Build Bf4, e3, Nf3, Bd3, castle, then choose c4 or e4.",
    "whyLearn": "London System gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Playing automatic moves without noticing ...c5 or ...Qb6 pressure."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bf4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bf4. This activates a bishop on a diagonal that supports the opening's central plan. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bd6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bd6. This activates a bishop on a diagonal that supports the opening's central plan. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "Bg3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg3. This activates a bishop on a diagonal that supports the opening's central plan. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 9,
        "san": "O-O",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays O-O. This moves the king out of the center and connects a rook, so the next central break is safer. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 10,
        "san": "Bd3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bd3. This activates a bishop on a diagonal that supports the opening's central plan. In the London System, connect it to the main idea: a repeatable development shell with a safe king and a timed e4 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "london-system-branch-1",
        "opponentMove": "2...c5",
        "answer": "e3",
        "explanation": "e3 keeps the center solid before deciding on c3 or c4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=London%20System%20beginner%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable London System video lesson"
    }
  },
  {
    "id": "scotch-game",
    "name": "Scotch Game",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "r1bqkb1r/pppp1ppp/2n2n2/8/3NP3/8/PPP2PPP/RNBQKB1R w KQkq - 1 5",
    "idea": "Open the center immediately and use rapid development to gain time.",
    "structure": "Open center with early piece contact",
    "plan": "Recapture with a piece, develop quickly, and avoid chasing pawns with the queen.",
    "whyLearn": "Scotch Game gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Trying to hold every central pawn instead of completing development."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "exd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Scotch Game, connect it to the main idea: open the center immediately and use rapid development to gain time. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "scotch-game-branch-1",
        "opponentMove": "4...Nf6",
        "answer": "Nxc6",
        "explanation": "Nxc6 can damage Black's structure when the timing is right. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Scotch%20Game%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Scotch Game video lesson"
    }
  },
  {
    "id": "ruy-lopez",
    "name": "Ruy Lopez",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "r1bqkb1r/1ppp1ppp/p1n2n2/4p3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 b kq - 3 5",
    "idea": "Pressure the defender of e5 and build a long-lasting central advantage.",
    "structure": "Closed or semi-open center with queenside tension",
    "plan": "Castle, play Re1 and c3, then choose d4 when e5 is adequately challenged.",
    "whyLearn": "Ruy Lopez gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Capturing on c6 automatically without understanding the pawn ending."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb5. This activates a bishop on a diagonal that supports the opening's central plan. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6. This improves coordination and prepares the next stage of the opening. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ba4. This activates a bishop on a diagonal that supports the opening's central plan. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O. This moves the king out of the center and connects a rook, so the next central break is safer. In the Ruy Lopez, connect it to the main idea: pressure the defender of e5 and build a long-lasting central advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "ruy-lopez-branch-1",
        "opponentMove": "3...Nf6",
        "answer": "O-O",
        "explanation": "O-O protects the king before deciding how to defend e4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Ruy Lopez video lesson"
    }
  },
  {
    "id": "vienna-game",
    "name": "Vienna Game",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqkb1r/ppp2ppp/8/3pP3/4n3/2N5/PPPP2PP/R1BQKBNR w KQkq - 0 5",
    "idea": "Keep flexible development while creating a kingside f-pawn lever.",
    "structure": "Open e- and f-files after central contact",
    "plan": "Develop Nc3, use f4 only when the center allows it, and bring Nf3 before attacking.",
    "whyLearn": "Vienna Game gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Launching f4 while the king remains in the center for too long."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "f4",
        "color": "white",
        "role": "player",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "fxe5",
        "color": "white",
        "role": "player",
        "explanation": "White plays fxe5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nxe4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Vienna Game, connect it to the main idea: keep flexible development while creating a kingside f-pawn lever. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "vienna-game-branch-1",
        "opponentMove": "2...Nf6",
        "answer": "f4",
        "explanation": "f4 creates the Vienna Gambit under favorable conditions. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Vienna%20Game%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Vienna Game video lesson"
    }
  },
  {
    "id": "kings-gambit",
    "name": "King's Gambit",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Advanced",
    "benchmark": 56,
    "simplicity": 2,
    "explorerFen": "rnbqkbnr/pppp1p1p/8/6p1/4Pp1P/5N2/PPPP2P1/RNBQKB1R b KQkq - 0 4",
    "idea": "Offer a pawn to open lines and seize development time against Black's king.",
    "structure": "Open f-file and unstable kingside pawns",
    "plan": "Develop with tempo, attack the pawn chain, and castle before the initiative fades.",
    "whyLearn": "King's Gambit gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Trying to win the gambit pawn back with the queen."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "f4",
        "color": "white",
        "role": "player",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "exf4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exf4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "g5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g5. This improves coordination and prepares the next stage of the opening. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "h4",
        "color": "white",
        "role": "player",
        "explanation": "White plays h4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the King's Gambit, connect it to the main idea: offer a pawn to open lines and seize development time against Black's king. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "kings-gambit-branch-1",
        "opponentMove": "2...exf4",
        "answer": "Nf3",
        "explanation": "Nf3 attacks e5 and prevents ...Qh4+. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=King's%20Gambit%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable King's Gambit video lesson"
    }
  },
  {
    "id": "queens-gambit",
    "name": "Queen's Gambit",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 56,
    "simplicity": 4,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/3p2B1/2PP4/2N5/PP2PPPP/R2QKBNR w KQkq - 4 5",
    "idea": "Challenge Black's d5 pawn to gain central space and freer development.",
    "structure": "Tense d4/d5 center",
    "plan": "Develop naturally, pressure d5, and choose e4 or a minority attack by structure.",
    "whyLearn": "Queen's Gambit gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Obsessing over recovering c4 instead of developing."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5. This activates a bishop on a diagonal that supports the opening's central plan. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7. This activates a bishop on a diagonal that supports the opening's central plan. In the Queen's Gambit, connect it to the main idea: challenge Black's d5 pawn to gain central space and freer development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "queens-gambit-branch-1",
        "opponentMove": "2...dxc4",
        "answer": "e3",
        "explanation": "e3 prepares to recover c4 with the bishop. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Queen's Gambit video lesson"
    }
  },
  {
    "id": "catalan",
    "name": "Catalan Opening",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/3p4/2PP4/5NP1/PP2PPBP/RNBQK2R b KQkq - 3 5",
    "idea": "Combine Queen's Gambit pressure with a powerful long diagonal.",
    "structure": "Closed center with long-diagonal pressure",
    "plan": "Fianchetto, castle, pressure c6/d5, and regain any c4 pawn without rushing.",
    "whyLearn": "Catalan Opening gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Trading the g2 bishop without a concrete gain."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2. This activates a bishop on a diagonal that supports the opening's central plan. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7. This activates a bishop on a diagonal that supports the opening's central plan. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Catalan Opening, connect it to the main idea: combine Queen's Gambit pressure with a powerful long diagonal. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "catalan-branch-1",
        "opponentMove": "3...d5",
        "answer": "Bg2",
        "explanation": "Bg2 completes the defining fianchetto. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Catalan%20Opening%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Catalan Opening video lesson"
    }
  },
  {
    "id": "english-opening",
    "name": "English Opening",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "c4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqkb1r/ppp2ppp/8/3np3/8/2N3P1/PP1PPP1P/R1BQKBNR w KQkq - 0 5",
    "idea": "Control d5 from the flank and keep several central structures available.",
    "structure": "Flexible reversed-Sicilian structure",
    "plan": "Fianchetto, castle, and choose d3 or d4 based on Black's setup.",
    "whyLearn": "English Opening gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Remaining too passive because the first move was a flank move."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "cxd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays cxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nxd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the English Opening, connect it to the main idea: control d5 from the flank and keep several central structures available. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "english-opening-branch-1",
        "opponentMove": "1...e5",
        "answer": "Nc3",
        "explanation": "Nc3 increases control over d5. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=English%20Opening%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable English Opening video lesson"
    }
  },
  {
    "id": "reti-opening",
    "name": "Réti Opening",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "flank",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/3p4/8/5NP1/PPPPPPBP/RNBQ1RK1 w kq - 2 5",
    "idea": "Invite a broad center, then attack it with pieces and pawn breaks.",
    "structure": "Hypermodern center with a kingside fianchetto",
    "plan": "Castle early, use c4 against d5, and avoid conceding space without counterplay.",
    "whyLearn": "Réti Opening gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Letting Black build e5 and d4 without challenging the center."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2. This activates a bishop on a diagonal that supports the opening's central plan. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O. This moves the king out of the center and connects a rook, so the next central break is safer. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7. This activates a bishop on a diagonal that supports the opening's central plan. In the Réti Opening, connect it to the main idea: invite a broad center, then attack it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "reti-opening-branch-1",
        "opponentMove": "1...d5",
        "answer": "g3",
        "explanation": "g3 prepares the bishop that will pressure the center. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=R%C3%A9ti%20Opening%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Réti Opening video lesson"
    }
  },
  {
    "id": "jobava-london",
    "name": "Jobava London",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkb1r/ppp2ppp/4pn2/1N1p4/3P1B2/8/PPP1PPPP/R2QKBNR b KQkq - 1 4",
    "idea": "Pair London development with Nc3 and fast pressure on c7.",
    "structure": "Compact center with tactical queenside pressure",
    "plan": "Develop Bf4 and Nc3, watch c7, but castle if the tactics are not real.",
    "whyLearn": "Jobava London gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Playing Nb5 when a6 can trap the knight."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bf4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bf4. This activates a bishop on a diagonal that supports the opening's central plan. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nb5. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Jobava London, connect it to the main idea: pair London development with Nc3 and fast pressure on c7. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "jobava-london-branch-1",
        "opponentMove": "2...Nf6",
        "answer": "Bf4",
        "explanation": "Bf4 reaches the Jobava setup. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Jobava%20London%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Jobava London video lesson"
    }
  },
  {
    "id": "trompowsky",
    "name": "Trompowsky Attack",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 50,
    "simplicity": 4,
    "explorerFen": "rnbqkb1r/ppp1pppp/8/3p4/3PnB2/4P3/PPP2PPP/RN1QKBNR b KQkq - 0 4",
    "idea": "Question the f6 knight before Black settles into a familiar defense.",
    "structure": "Flexible center with doubled-pawn possibilities",
    "plan": "Use the bishop to provoke a concession, then build e3 and Nd2.",
    "whyLearn": "Trompowsky Attack gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Giving up the bishop pair without damaging structure or gaining time."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5. This activates a bishop on a diagonal that supports the opening's central plan. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Ne4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Ne4. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bf4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bf4. This activates a bishop on a diagonal that supports the opening's central plan. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Trompowsky Attack, connect it to the main idea: question the f6 knight before Black settles into a familiar defense. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "trompowsky-branch-1",
        "opponentMove": "2...Ne4",
        "answer": "Bf4",
        "explanation": "Bf4 keeps the bishop active and controls c7. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Trompowsky%20Attack%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Trompowsky Attack video lesson"
    }
  },
  {
    "id": "colle-system",
    "name": "Colle System",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/2pp4/3P4/3BPN2/PPP2PPP/RNBQ1RK1 b kq - 1 5",
    "idea": "Build safely, then prepare the thematic e4 central break.",
    "structure": "Closed center that can open with e4",
    "plan": "Develop Bd3, castle, play Nbd2 and prepare e4 with enough support.",
    "whyLearn": "Colle System gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Playing e4 before it is tactically supported."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Bd3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bd3. This activates a bishop on a diagonal that supports the opening's central plan. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O. This moves the king out of the center and connects a rook, so the next central break is safer. In the Colle System, connect it to the main idea: build safely, then prepare the thematic e4 central break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "colle-system-branch-1",
        "opponentMove": "2...Nf6",
        "answer": "e3",
        "explanation": "e3 opens the bishop and supports d4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Colle%20System%20beginner%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Colle System video lesson"
    }
  },
  {
    "id": "birds-opening",
    "name": "Bird Opening",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "flank",
    "complexity": "Simple",
    "benchmark": 50,
    "simplicity": 4,
    "explorerFen": "rnbqk2r/ppp1ppbp/5np1/3p4/5P2/1P2PN2/PBPP2PP/RN1QKB1R b KQkq - 2 5",
    "idea": "Control e5 immediately and build a kingside space advantage.",
    "structure": "Dutch structure with colors reversed",
    "plan": "Develop Nf3, b3/Bb2, castle, and only then expand with kingside pawns.",
    "whyLearn": "Bird Opening gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Weakening the king with more f-pawn moves before castling."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "f4",
        "color": "white",
        "role": "player",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "b3",
        "color": "white",
        "role": "player",
        "explanation": "White plays b3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "Bb2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb2. This activates a bishop on a diagonal that supports the opening's central plan. In the Bird Opening, connect it to the main idea: control e5 immediately and build a kingside space advantage. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "birds-opening-branch-1",
        "opponentMove": "1...d5",
        "answer": "Nf3",
        "explanation": "Nf3 controls e5 and develops. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Bird%20Opening%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Bird Opening video lesson"
    }
  },
  {
    "id": "grand-prix-attack",
    "name": "Grand Prix Attack vs Sicilian",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 53,
    "simplicity": 4,
    "explorerFen": "r1bqk1nr/pp1pppbp/2n3p1/2p5/4PP2/2N2N2/PPPP2PP/R1BQKB1R w KQkq - 2 5",
    "idea": "Use f4 and rapid kingside development against the Sicilian.",
    "structure": "Closed center with kingside space",
    "plan": "Develop Nf3, Bc4 or Bb5, castle, then use f5 only when pieces are ready.",
    "whyLearn": "Grand Prix Attack vs Sicilian gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Pushing f5 before the queen and bishop can join."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "f4",
        "color": "white",
        "role": "player",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the Grand Prix Attack vs Sicilian, connect it to the main idea: use f4 and rapid kingside development against the Sicilian. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "grand-prix-attack-branch-1",
        "opponentMove": "2...Nc6",
        "answer": "f4",
        "explanation": "f4 claims e5 and signals the attack. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Grand%20Prix%20Attack%20vs%20Sicilian%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Grand Prix Attack vs Sicilian video lesson"
    }
  },
  {
    "id": "alapin-sicilian",
    "name": "Alapin Sicilian",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkb1r/pp1ppppp/8/2pnP3/3P4/2P5/PP3PPP/RNBQKBNR b KQkq - 0 4",
    "idea": "Build a broad d4/e4 center while avoiding heavy Sicilian theory.",
    "structure": "Broad pawn center under immediate attack",
    "plan": "Support e5, develop, and accept that an isolated queen pawn can give activity.",
    "whyLearn": "Alapin Sicilian gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Defending the center with too many pawn moves and falling behind."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c3",
        "color": "white",
        "role": "player",
        "explanation": "White plays c3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "e5",
        "color": "white",
        "role": "player",
        "explanation": "White plays e5. This improves coordination and prepares the next stage of the opening. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nd5. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Alapin Sicilian, connect it to the main idea: build a broad d4/e4 center while avoiding heavy Sicilian theory. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "alapin-sicilian-branch-1",
        "opponentMove": "2...Nf6",
        "answer": "e5",
        "explanation": "e5 gains space while attacking the knight. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Alapin%20Sicilian%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Alapin Sicilian video lesson"
    }
  },
  {
    "id": "smith-morra",
    "name": "Smith–Morra Gambit",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Advanced",
    "benchmark": 50,
    "simplicity": 2,
    "explorerFen": "rnbqkbnr/pp1ppppp/8/8/4P3/2N5/PP3PPP/R1BQKBNR b KQkq - 0 4",
    "idea": "Sacrifice a pawn for open files and fast development.",
    "structure": "Open c- and d-files with a development lead",
    "plan": "Place rooks on c1 and d1, develop Bc4, and use tactics before Black consolidates.",
    "whyLearn": "Smith–Morra Gambit gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Trading pieces when the compensation depends on activity."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "cxd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "c3",
        "color": "white",
        "role": "player",
        "explanation": "White plays c3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "dxc3",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc3. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nxc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxc3. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Smith–Morra Gambit, connect it to the main idea: sacrifice a pawn for open files and fast development. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "smith-morra-branch-1",
        "opponentMove": "2...cxd4",
        "answer": "c3",
        "explanation": "c3 offers the Morra pawn for development. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Smith%E2%80%93Morra%20Gambit%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Smith–Morra Gambit video lesson"
    }
  },
  {
    "id": "advance-french",
    "name": "French Advance",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "r1bqkbnr/pp3ppp/2n1p3/2ppP3/3P4/2P5/PP3PPP/RNBQKBNR w KQkq - 1 5",
    "idea": "Gain space with e5 and defend the pawn chain at its base.",
    "structure": "Locked e5/d4 chain versus c5/f6 breaks",
    "plan": "Support d4 with c3, develop, and attack on the side where you have space.",
    "whyLearn": "French Advance gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Defending e5 while ignoring pressure on d4."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "e5",
        "color": "white",
        "role": "player",
        "explanation": "White plays e5. This improves coordination and prepares the next stage of the opening. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "c3",
        "color": "white",
        "role": "player",
        "explanation": "White plays c3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the French Advance, connect it to the main idea: gain space with e5 and defend the pawn chain at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "advance-french-branch-1",
        "opponentMove": "3...c5",
        "answer": "c3",
        "explanation": "c3 reinforces d4, the chain's base. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Advance%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Advance video lesson"
    }
  },
  {
    "id": "exchange-french",
    "name": "French Exchange",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkbnr/ppp2ppp/8/3p4/3P4/8/PPP2PPP/RNBQKBNR w KQkq - 0 4",
    "idea": "Clarify the center and play an open, development-focused game.",
    "structure": "Symmetrical open e-file structure",
    "plan": "Develop actively, use Bd3 and Ne2, and create imbalance with c4 when useful.",
    "whyLearn": "French Exchange gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Assuming symmetry means there is no plan."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Exchange, connect it to the main idea: clarify the center and play an open, development-focused game. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the French Exchange, connect it to the main idea: clarify the center and play an open, development-focused game. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Exchange, connect it to the main idea: clarify the center and play an open, development-focused game. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the French Exchange, connect it to the main idea: clarify the center and play an open, development-focused game. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "exd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays exd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the French Exchange, connect it to the main idea: clarify the center and play an open, development-focused game. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "exd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the French Exchange, connect it to the main idea: clarify the center and play an open, development-focused game. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "exchange-french-branch-1",
        "opponentMove": "3...exd5",
        "answer": "Bd3",
        "explanation": "Bd3 places the bishop on its best attacking diagonal. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Exchange%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Exchange video lesson"
    }
  },
  {
    "id": "panov-attack",
    "name": "Panov Attack vs Caro–Kann",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 52,
    "simplicity": 5,
    "explorerFen": "rnbqkbnr/pp2pppp/8/3p4/2PP4/8/PP3PPP/RNBQKBNR b KQkq - 0 4",
    "idea": "Turn the Caro–Kann into an active isolated-queen-pawn position.",
    "structure": "Isolated d-pawn potential with open piece play",
    "plan": "Develop Nc3 and Nf3, use active pieces, and time d5 before exchanges favor Black.",
    "whyLearn": "Panov Attack vs Caro–Kann gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Trading all active pieces and keeping only the isolated pawn."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6. This improves coordination and prepares the next stage of the opening. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "exd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays exd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "cxd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Panov Attack vs Caro–Kann, connect it to the main idea: turn the Caro–Kann into an active isolated-queen-pawn position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "panov-attack-branch-1",
        "opponentMove": "3...cxd5",
        "answer": "c4",
        "explanation": "c4 attacks d5 immediately. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Panov%20Attack%20vs%20Caro%E2%80%93Kann%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Panov Attack vs Caro–Kann video lesson"
    }
  },
  {
    "id": "fantasy-variation",
    "name": "Fantasy Variation vs Caro–Kann",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 52,
    "simplicity": 5,
    "explorerFen": "rnbqkbnr/pp3ppp/2p1p3/3p4/3PP3/2N2P2/PPP3PP/R1BQKBNR b KQkq - 1 4",
    "idea": "Support e4 with f3 and keep a large center.",
    "structure": "Broad center with a slightly exposed king",
    "plan": "Develop Nc3 and Be3, choose e5 or exd5, and castle queenside only after checking tactics.",
    "whyLearn": "Fantasy Variation vs Caro–Kann gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Starting a pawn storm before the king has a safe destination."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6. This improves coordination and prepares the next stage of the opening. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "f3",
        "color": "white",
        "role": "player",
        "explanation": "White plays f3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Fantasy Variation vs Caro–Kann, connect it to the main idea: support e4 with f3 and keep a large center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "fantasy-variation-branch-1",
        "opponentMove": "3...e6",
        "answer": "Nc3",
        "explanation": "Nc3 reinforces the center. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Fantasy%20Variation%20vs%20Caro%E2%80%93Kann%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Fantasy Variation vs Caro–Kann video lesson"
    }
  },
  {
    "id": "austrian-attack",
    "name": "Austrian Attack vs Pirc",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Advanced",
    "benchmark": 49,
    "simplicity": 2,
    "explorerFen": "rnbqk2r/ppp1ppbp/3p1np1/8/3PPP2/2N5/PPP3PP/R1BQKBNR w KQkq - 1 5",
    "idea": "Build a large center and use f4 to claim attacking space.",
    "structure": "Broad e4/d4 center versus hypermodern pressure",
    "plan": "Develop Nf3, Be3 and Qd2, castle, then choose e5 or f5 from a secure base.",
    "whyLearn": "Austrian Attack vs Pirc gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Pushing e5 and f5 without completing development."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "f4",
        "color": "white",
        "role": "player",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the Austrian Attack vs Pirc, connect it to the main idea: build a large center and use f4 to claim attacking space. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "austrian-attack-branch-1",
        "opponentMove": "3...g6",
        "answer": "f4",
        "explanation": "f4 establishes the Austrian setup. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Austrian%20Attack%20vs%20Pirc%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Austrian Attack vs Pirc video lesson"
    }
  },
  {
    "id": "mainline-scandinavian",
    "name": "Main Line vs Scandinavian",
    "side": "White",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 53,
    "simplicity": 5,
    "explorerFen": "rnbqkbnr/ppp1pppp/8/8/3P4/2N5/PPP2PPP/R1BQKBNR b KQkq - 0 4",
    "idea": "Gain time on Black's exposed queen and occupy the center.",
    "structure": "Open center with a development lead",
    "plan": "Develop Nc3 with tempo, claim d4, and avoid hunting the queen beyond useful development.",
    "whyLearn": "Main Line vs Scandinavian gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Chasing the queen with pawns that weaken your own position."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "exd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays exd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Qxd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Qd8",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qd8. This places the queen where it supports a concrete threat; early queen moves should always have this specific justification. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Main Line vs Scandinavian, connect it to the main idea: gain time on Black's exposed queen and occupy the center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "mainline-scandinavian-branch-1",
        "opponentMove": "2...Qxd5",
        "answer": "Nc3",
        "explanation": "Nc3 develops while attacking the queen. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Main%20Line%20vs%20Scandinavian%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Main Line vs Scandinavian video lesson"
    }
  },
  {
    "id": "white-sicilian-defense-closed-11hr7",
    "name": "Sicilian Defense: Closed",
    "side": "White",
    "tier": "free",
    "eco": "B25",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk1nr/pp2ppbp/2np2p1/2p5/4P3/2NP2P1/PPP2PBP/R1BQK1NR w KQkq - 0 6",
    "idea": "Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Sicilian Defense: Closed is identified by the canonical ECO B25 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Closed as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "player",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-sicilian-defense-closed-11hr7-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Closed%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Closed video lesson"
    }
  },
  {
    "id": "white-sicilian-defense-pin-variation-puihc",
    "name": "Sicilian Defense: Pin Variation",
    "side": "White",
    "tier": "free",
    "eco": "B40",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/pp1p1ppp/4pn2/8/1b1NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 3 6",
    "idea": "Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Sicilian Defense: Pin Variation is identified by the canonical ECO B40 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Pin Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bb4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Sicilian Defense: Pin Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-sicilian-defense-pin-variation-puihc-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Pin%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Pin Variation video lesson"
    }
  },
  {
    "id": "white-sicilian-defense-dragon-variation-7wrua",
    "name": "Sicilian Defense: Dragon Variation",
    "side": "White",
    "tier": "free",
    "eco": "B70",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp2pp1p/3p1np1/8/3NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 0 6",
    "idea": "Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Sicilian Defense: Dragon Variation is identified by the canonical ECO B70 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Dragon Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-sicilian-defense-dragon-variation-7wrua-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Dragon%20Variation%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Sicilian Defense: Dragon Variation video lesson"
    }
  },
  {
    "id": "white-sicilian-defense-open-14fcc",
    "name": "Sicilian Defense: Open",
    "side": "White",
    "tier": "free",
    "eco": "B33",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pp1ppppp/2n2n2/8/3NP3/8/PPP2PPP/RNBQKB1R w KQkq - 1 5",
    "idea": "Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Sicilian Defense: Open is identified by the canonical ECO B33 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Open as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Open, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-sicilian-defense-open-14fcc-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Open%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Open video lesson"
    }
  },
  {
    "id": "white-sicilian-defense-gaw-paw-variation-1haqg",
    "name": "Sicilian Defense: Gaw-Paw Variation",
    "side": "White",
    "tier": "free",
    "eco": "B40",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1kb1r/pp1p1ppp/1q2pn2/8/3NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 3 6",
    "idea": "Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Sicilian Defense: Gaw-Paw Variation is identified by the canonical ECO B40 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Gaw-Paw Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Qb6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qb6 from d8 to b6. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Use the Sicilian Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-sicilian-defense-gaw-paw-variation-1haqg-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Gaw-Paw%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Gaw-Paw Variation video lesson"
    }
  },
  {
    "id": "white-pterodactyl-defense-sicilian-unpin-1rj4y",
    "name": "Pterodactyl Defense: Sicilian, Unpin",
    "side": "White",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1pppbp/6p1/q1p5/3PP3/2N2N2/PPPB1PPP/R2QKB1R b KQkq - 4 5",
    "idea": "Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Unpin is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Unpin as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bd2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bd2 from c1 to d2. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-pterodactyl-defense-sicilian-unpin-1rj4y-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Unpin%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Unpin video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-declined-12np5",
    "name": "Queen's Gambit Declined",
    "side": "White",
    "tier": "free",
    "eco": "D53",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/6B1/2pP4/2N2N2/PP2PPPP/R2QKB1R w KQkq - 2 6",
    "idea": "Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Declined is identified by the canonical ECO D53 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "dxc4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-declined-12np5-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Queen's Gambit Declined video lesson"
    }
  },
  {
    "id": "white-pterodactyl-defense-sicilian-quetzalcoatlus-1kzz4",
    "name": "Pterodactyl Defense: Sicilian, Quetzalcoatlus",
    "side": "White",
    "tier": "free",
    "eco": "B06",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp2ppbp/3p2p1/q1p5/3PP3/2N2N2/PPP1BPPP/R1BQK2R w KQkq - 0 6",
    "idea": "Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Quetzalcoatlus is identified by the canonical ECO B06 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Quetzalcoatlus as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Be2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Be2 from f1 to e2. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-pterodactyl-defense-sicilian-quetzalcoatlus-1kzz4-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Quetzalcoatlus%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Quetzalcoatlus video lesson"
    }
  },
  {
    "id": "white-king-s-indian-attack-sicilian-variation-xwdq3",
    "name": "King's Indian Attack: Sicilian Variation",
    "side": "White",
    "tier": "free",
    "eco": "A08",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/2pp4/8/3P1NP1/PPP1PPBP/RNBQ1RK1 b kq - 0 5",
    "idea": "Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "King's Indian Attack: Sicilian Variation is identified by the canonical ECO A08 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: Sicilian Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "player",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-king-s-indian-attack-sicilian-variation-xwdq3-branch-1",
        "opponentMove": "1...c5",
        "answer": "Nd4",
        "explanation": "Nd4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20Sicilian%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack: Sicilian Variation video lesson"
    }
  },
  {
    "id": "white-pterodactyl-defense-sicilian-anhanguera-12zh3",
    "name": "Pterodactyl Defense: Sicilian, Anhanguera",
    "side": "White",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1pppbp/6p1/q1p5/3PP3/2N1BN2/PPP2PPP/R2QKB1R b KQkq - 4 5",
    "idea": "Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Anhanguera is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Anhanguera as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Be3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Be3 from c1 to e3. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-pterodactyl-defense-sicilian-anhanguera-12zh3-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Anhanguera%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Anhanguera video lesson"
    }
  },
  {
    "id": "white-pterodactyl-defense-sicilian-pteranodon-1frt3",
    "name": "Pterodactyl Defense: Sicilian, Pteranodon",
    "side": "White",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1ppp1p/6p1/q1P5/4P3/2P2N2/P1P2PPP/R1BQKB1R b KQkq - 0 6",
    "idea": "Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Pteranodon is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Pteranodon as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "dxc5",
        "color": "white",
        "role": "player",
        "explanation": "White plays dxc5 from d4 to c5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5+",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qa5+ from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bxc3+",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bxc3+ from g7 to c3. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "bxc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays bxc3 from b2 to c3. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-pterodactyl-defense-sicilian-pteranodon-1frt3-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Pteranodon%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Pteranodon video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-accepted-c611s",
    "name": "Queen's Gambit Accepted",
    "side": "White",
    "tier": "free",
    "eco": "D24",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/ppp2ppp/4pn2/8/2pPP3/2N2N2/PP3PPP/R1BQKB1R b KQkq - 0 5",
    "idea": "Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Accepted is identified by the canonical ECO D24 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "dxc4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-accepted-c611s-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted video lesson"
    }
  },
  {
    "id": "white-pterodactyl-defense-sicilian-benoni-gambit-1pdy5",
    "name": "Pterodactyl Defense: Sicilian, Benoni Gambit",
    "side": "White",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1pppbp/6p1/q1pP4/4P3/2N2N2/PPP2PPP/R1BQKB1R b KQkq - 0 5",
    "idea": "Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Benoni Gambit is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Benoni Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d5",
        "color": "white",
        "role": "player",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Use the Pterodactyl Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-pterodactyl-defense-sicilian-benoni-gambit-1pdy5-branch-1",
        "opponentMove": "1...d5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Benoni%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Benoni Gambit video lesson"
    }
  },
  {
    "id": "white-van-geet-opening-sicilian-two-knights-17qhi",
    "name": "Van Geet Opening: Sicilian Two Knights",
    "side": "White",
    "tier": "free",
    "eco": "A00",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nc3",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "r1bqkbnr/pp1ppppp/2n5/8/3N4/2N5/PPP1PPPP/R1BQKB1R b KQkq - 0 4",
    "idea": "Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Van Geet Opening: Sicilian Two Knights is identified by the canonical ECO A00 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Van Geet Opening: Sicilian Two Knights as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Use the Van Geet Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-van-geet-opening-sicilian-two-knights-17qhi-branch-1",
        "opponentMove": "1...d5",
        "answer": "Nxd5",
        "explanation": "Nxd5 is a legal, practical reply to d5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Van%20Geet%20Opening%3A%20Sicilian%20Two%20Knights%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Van Geet Opening: Sicilian Two Knights video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-declined-lasker-defense-1mj87",
    "name": "Queen's Gambit Declined: Lasker Defense",
    "side": "White",
    "tier": "free",
    "eco": "D53",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4p3/3p2B1/2PPn3/2N1P3/PP3PPP/R2QKBNR w KQkq - 1 6",
    "idea": "Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Declined: Lasker Defense is identified by the canonical ECO D53 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Lasker Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Ne4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Ne4 from f6 to e4. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-declined-lasker-defense-1mj87-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Lasker%20Defense%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Queen's Gambit Declined: Lasker Defense video lesson"
    }
  },
  {
    "id": "white-benoni-defense-franco-sicilian-hybrid-1geqx",
    "name": "Benoni Defense: Franco-Sicilian Hybrid",
    "side": "White",
    "tier": "free",
    "eco": "A40",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/pp2npbp/3p2p1/2pP4/4P3/2N2N2/PP3PPP/R1BQKB1R w KQkq - 3 8",
    "idea": "Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Benoni Defense: Franco-Sicilian Hybrid is identified by the canonical ECO A40 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Benoni Defense: Franco-Sicilian Hybrid as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d5",
        "color": "white",
        "role": "player",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "exd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exd5 from e6 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "cxd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays cxd5 from c4 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 11,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 12,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 13,
        "san": "Ne7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Ne7 from g8 to e7. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-benoni-defense-franco-sicilian-hybrid-1geqx-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Benoni%20Defense%3A%20Franco-Sicilian%20Hybrid%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Benoni Defense: Franco-Sicilian Hybrid video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-accepted-classical-defense-6al4w",
    "name": "Queen's Gambit Accepted: Classical Defense",
    "side": "White",
    "tier": "free",
    "eco": "D26",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/2p5/2BP4/4PN2/PP3PPP/RNBQK2R w KQkq - 0 6",
    "idea": "Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Accepted: Classical Defense is identified by the canonical ECO D26 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Classical Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bxc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bxc4 from f1 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-accepted-classical-defense-6al4w-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Classical%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Classical Defense video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-accepted-linares-variation-9a6sx",
    "name": "Queen's Gambit Accepted: Linares Variation",
    "side": "White",
    "tier": "free",
    "eco": "D20",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/p3pppp/5n2/1ppP4/2p1P3/2N5/PP3PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Accepted: Linares Variation is identified by the canonical ECO D20 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Linares Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "d5",
        "color": "white",
        "role": "player",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "b5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays b5 from b7 to b5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-accepted-linares-variation-9a6sx-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Linares%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Linares Variation video lesson"
    }
  },
  {
    "id": "white-english-opening-mikenas-carls-sicilian-1ij1j",
    "name": "English Opening: Mikenas-Carls, Sicilian",
    "side": "White",
    "tier": "free",
    "eco": "A19",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "c4",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp1p1ppp/4pn2/2p5/2P1P3/2N5/PP1P1PPP/R1BQKBNR w KQkq - 0 4",
    "idea": "Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "English Opening: Mikenas-Carls, Sicilian is identified by the canonical ECO A19 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name English Opening: Mikenas-Carls, Sicilian as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-english-opening-mikenas-carls-sicilian-1ij1j-branch-1",
        "opponentMove": "1...c5",
        "answer": "d4",
        "explanation": "d4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=English%20Opening%3A%20Mikenas-Carls%2C%20Sicilian%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable English Opening: Mikenas-Carls, Sicilian video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-declined-manhattan-variation-1kla4",
    "name": "Queen's Gambit Declined: Manhattan Variation",
    "side": "White",
    "tier": "free",
    "eco": "D51",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppn1ppp/4pn2/3p2B1/1bPP4/2N1P3/PP3PPP/R2QKBNR w KQkq - 1 6",
    "idea": "Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Declined: Manhattan Variation is identified by the canonical ECO D51 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Manhattan Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nbd7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nbd7 from b8 to d7. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bb4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-declined-manhattan-variation-1kla4-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Manhattan%20Variation%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Queen's Gambit Declined: Manhattan Variation video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-declined-spielmann-variation-oaphx",
    "name": "Queen's Gambit Declined: Spielmann Variation",
    "side": "White",
    "tier": "free",
    "eco": "D30",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3p1p/2p1pnp1/3p4/2PP4/4PN2/PP1N1PPP/R1BQKB1R w KQkq - 0 6",
    "idea": "Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Declined: Spielmann Variation is identified by the canonical ECO D30 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Spielmann Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nbd2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nbd2 from b1 to d2. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-declined-spielmann-variation-oaphx-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Spielmann%20Variation%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Queen's Gambit Declined: Spielmann Variation video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-declined-harrwitz-attack-1hhhb",
    "name": "Queen's Gambit Declined: Harrwitz Attack",
    "side": "White",
    "tier": "free",
    "eco": "D37",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/3p4/2PP1B2/2N2N2/PP2PPPP/R2QKB1R b KQkq - 3 5",
    "idea": "Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Declined: Harrwitz Attack is identified by the canonical ECO D37 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Harrwitz Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bf4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bf4 from c1 to f4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Use the Queen's Gambit Declined move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-declined-harrwitz-attack-1hhhb-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Harrwitz%20Attack%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Declined: Harrwitz Attack video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-accepted-bogoljubow-defense-1ez93",
    "name": "Queen's Gambit Accepted: Bogoljubow Defense",
    "side": "White",
    "tier": "free",
    "eco": "D24",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/1pp1pppp/p4n2/8/2pPP3/2N2N2/PP3PPP/R1BQKB1R b KQkq - 0 5",
    "idea": "Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Accepted: Bogoljubow Defense is identified by the canonical ECO D24 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Bogoljubow Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-accepted-bogoljubow-defense-1ez93-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Bogoljubow%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Bogoljubow Defense video lesson"
    }
  },
  {
    "id": "white-italian-game-giuoco-pianissimo-7nzcq",
    "name": "Italian Game: Giuoco Pianissimo",
    "side": "White",
    "tier": "free",
    "eco": "C50",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bq1rk1/pppp1ppp/2n2n2/2b1p3/2B1P3/2N2N2/PPPP1PPP/R1BQ1RK1 w - - 8 6",
    "idea": "Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Italian Game: Giuoco Pianissimo is identified by the canonical ECO C50 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Giuoco Pianissimo as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "O-O",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays O-O from e8 to g8. The move secures the king and connects the rooks before the center opens. In Italian Game: Giuoco Pianissimo, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-italian-game-giuoco-pianissimo-7nzcq-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Giuoco%20Pianissimo%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Italian Game: Giuoco Pianissimo video lesson"
    }
  },
  {
    "id": "white-italian-game-deutz-gambit-10fl2",
    "name": "Italian Game: Deutz Gambit",
    "side": "White",
    "tier": "free",
    "eco": "C50",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/2b1p3/2BPP3/5N2/PPP2PPP/RNBQ1RK1 b kq - 0 5",
    "idea": "Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Italian Game: Deutz Gambit is identified by the canonical ECO C50 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Deutz Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Deutz Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-italian-game-deutz-gambit-10fl2-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Deutz%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Italian Game: Deutz Gambit video lesson"
    }
  },
  {
    "id": "white-queen-s-gambit-accepted-winawer-defense-1ibnd",
    "name": "Queen's Gambit Accepted: Winawer Defense",
    "side": "White",
    "tier": "free",
    "eco": "D25",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rn1qkb1r/ppp1pppp/4bn2/8/2pP4/4PN2/PP3PPP/RNBQKB1R w KQkq - 1 5",
    "idea": "Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Queen's Gambit Accepted: Winawer Defense is identified by the canonical ECO D25 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Winawer Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "player",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be6 from c8 to e6. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Use the Queen's Gambit Accepted move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-queen-s-gambit-accepted-winawer-defense-1ibnd-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Winawer%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Winawer Defense video lesson"
    }
  },
  {
    "id": "white-english-opening-king-s-english-variation-rever-1i52y",
    "name": "English Opening: King's English Variation, Reversed Closed Sicilian",
    "side": "White",
    "tier": "free",
    "eco": "A25",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "c4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/3Np3/1bP5/6P1/PP1PPPBP/R1BQK1NR b KQkq - 6 5",
    "idea": "Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "English Opening: King's English Variation, Reversed Closed Sicilian is identified by the canonical ECO A25 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name English Opening: King's English Variation, Reversed Closed Sicilian as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bb4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nd5 from c3 to d5. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Use the English Opening move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-english-opening-king-s-english-variation-rever-1i52y-branch-1",
        "opponentMove": "1...c5",
        "answer": "d4",
        "explanation": "d4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=English%20Opening%3A%20King's%20English%20Variation%2C%20Reversed%20Closed%20Sicilian%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable English Opening: King's English Variation, Reversed Closed Sicilian video lesson"
    }
  },
  {
    "id": "white-italian-game-bird-s-attack-16s21",
    "name": "Italian Game: Bird's Attack",
    "side": "White",
    "tier": "free",
    "eco": "C53",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/2b1p3/1PB1P3/2P2N2/P2P1PPP/RNBQK2R b KQkq - 0 5",
    "idea": "Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Italian Game: Bird's Attack is identified by the canonical ECO C53 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Bird's Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "c3",
        "color": "white",
        "role": "player",
        "explanation": "White plays c3 from c2 to c3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "b4",
        "color": "white",
        "role": "player",
        "explanation": "White plays b4 from b2 to b4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Bird's Attack, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-italian-game-bird-s-attack-16s21-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Bird's%20Attack%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Italian Game: Bird's Attack video lesson"
    }
  },
  {
    "id": "white-italian-game-scotch-gambit-3ehx8",
    "name": "Italian Game: Scotch Gambit",
    "side": "White",
    "tier": "free",
    "eco": "C56",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pppp1ppp/2n2n2/8/2BpP3/5N2/PPP2PPP/RNBQ1RK1 b kq - 1 5",
    "idea": "Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Italian Game: Scotch Gambit is identified by the canonical ECO C56 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Scotch Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "exd4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exd4 from e5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Italian Game: Scotch Gambit, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-italian-game-scotch-gambit-3ehx8-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Scotch%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Italian Game: Scotch Gambit video lesson"
    }
  },
  {
    "id": "white-italian-game-two-knights-defense-7nj4j",
    "name": "Italian Game: Two Knights Defense",
    "side": "White",
    "tier": "free",
    "eco": "C55",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/ppp2ppp/2n5/3pp3/2B1N3/5N2/PPPP1PPP/R1BQK2R w KQkq - 0 6",
    "idea": "Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Italian Game: Two Knights Defense is identified by the canonical ECO C55 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Two Knights Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nxe4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Two Knights Defense, relate it to this course objective: Use the Italian Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-italian-game-two-knights-defense-7nj4j-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Two%20Knights%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Italian Game: Two Knights Defense video lesson"
    }
  },
  {
    "id": "white-ruy-lopez-open-1ex87",
    "name": "Ruy Lopez: Open",
    "side": "White",
    "tier": "free",
    "eco": "C80",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/1ppp1ppp/p1n5/4p3/B3n3/5N2/PPPP1PPP/RNBQ1RK1 w kq - 0 6",
    "idea": "Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Ruy Lopez: Open is identified by the canonical ECO C80 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Open as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Nxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Ruy Lopez: Open, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-ruy-lopez-open-1ex87-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Open%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Ruy Lopez: Open video lesson"
    }
  },
  {
    "id": "white-ruy-lopez-closed-is9d2",
    "name": "Ruy Lopez: Closed",
    "side": "White",
    "tier": "free",
    "eco": "C84",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/1pppbppp/p1n2n2/4p3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 w kq - 4 6",
    "idea": "Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Ruy Lopez: Closed is identified by the canonical ECO C84 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Closed as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Closed, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-ruy-lopez-closed-is9d2-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Closed%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Ruy Lopez: Closed video lesson"
    }
  },
  {
    "id": "white-ruy-lopez-brix-variation-16o3n",
    "name": "Ruy Lopez: Brix Variation",
    "side": "White",
    "tier": "free",
    "eco": "C78",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/1ppp1p1p/p1n2np1/4p3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 w kq - 0 6",
    "idea": "Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Ruy Lopez: Brix Variation is identified by the canonical ECO C78 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Brix Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Brix Variation, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-ruy-lopez-brix-variation-16o3n-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Brix%20Variation%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Ruy Lopez: Brix Variation video lesson"
    }
  },
  {
    "id": "white-four-knights-game-italian-variation-1l7ge",
    "name": "Four Knights Game: Italian Variation",
    "side": "White",
    "tier": "free",
    "eco": "C50",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/2b1p3/2B1P3/2N2N2/PPPP1PPP/R1BQK2R w KQkq - 6 5",
    "idea": "Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Four Knights Game: Italian Variation is identified by the canonical ECO C50 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Four Knights Game: Italian Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-four-knights-game-italian-variation-1l7ge-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Four%20Knights%20Game%3A%20Italian%20Variation%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Four Knights Game: Italian Variation video lesson"
    }
  },
  {
    "id": "white-ruy-lopez-morphy-defense-1bhbq",
    "name": "Ruy Lopez: Morphy Defense",
    "side": "White",
    "tier": "free",
    "eco": "C78",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/1ppp1ppp/p1n2n2/4p3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 b kq - 3 5",
    "idea": "Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Ruy Lopez: Morphy Defense is identified by the canonical ECO C78 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Morphy Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Morphy Defense, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-ruy-lopez-morphy-defense-1bhbq-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Morphy%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Ruy Lopez: Morphy Defense video lesson"
    }
  },
  {
    "id": "white-ruy-lopez-central-countergambit-5tikr",
    "name": "Ruy Lopez: Central Countergambit",
    "side": "White",
    "tier": "free",
    "eco": "C78",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/1pp2ppp/p1n2n2/3pp3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 w kq - 0 6",
    "idea": "Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Ruy Lopez: Central Countergambit is identified by the canonical ECO C78 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Central Countergambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Use the Ruy Lopez move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-ruy-lopez-central-countergambit-5tikr-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Central%20Countergambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Ruy Lopez: Central Countergambit video lesson"
    }
  },
  {
    "id": "white-four-knights-game-italian-variation-noa-gambit-93n8u",
    "name": "Four Knights Game: Italian Variation, Noa Gambit",
    "side": "White",
    "tier": "free",
    "eco": "C47",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pppp1Bpp/2n5/4p3/4n3/2N2N2/PPPP1PPP/R1BQK2R b KQkq - 0 5",
    "idea": "Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Four Knights Game: Italian Variation, Noa Gambit is identified by the canonical ECO C47 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Four Knights Game: Italian Variation, Noa Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bxf7+",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bxf7+ from c4 to f7. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Use the Four Knights Game move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-four-knights-game-italian-variation-noa-gambit-93n8u-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Four%20Knights%20Game%3A%20Italian%20Variation%2C%20Noa%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Four Knights Game: Italian Variation, Noa Gambit video lesson"
    }
  },
  {
    "id": "white-french-defense-steinitz-variation-826sz",
    "name": "French Defense: Steinitz Variation",
    "side": "White",
    "tier": "free",
    "eco": "C11",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/1ppn1ppp/p3p3/3pP3/3P4/2N2N2/PPP2PPP/R1BQKB1R w KQkq - 1 6",
    "idea": "Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "French Defense: Steinitz Variation is identified by the canonical ECO C11 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Steinitz Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e5",
        "color": "white",
        "role": "player",
        "explanation": "White plays e5 from e4 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Nfd7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nfd7 from f6 to d7. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-french-defense-steinitz-variation-826sz-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Steinitz%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable French Defense: Steinitz Variation video lesson"
    }
  },
  {
    "id": "white-french-defense-classical-variation-149ge",
    "name": "French Defense: Classical Variation",
    "side": "White",
    "tier": "free",
    "eco": "C13",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/6B1/3PN3/8/PPP2PPP/R2QKBNR w KQkq - 1 6",
    "idea": "Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "French Defense: Classical Variation is identified by the canonical ECO C13 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Classical Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "dxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nxe4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Classical Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-french-defense-classical-variation-149ge-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Classical%20Variation%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Defense: Classical Variation video lesson"
    }
  },
  {
    "id": "white-petrov-s-defense-french-attack-8j0gy",
    "name": "Petrov's Defense: French Attack",
    "side": "White",
    "tier": "free",
    "eco": "C42",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/ppp2ppp/3p4/8/4n3/3P1N2/PPP2PPP/RNBQKB1R b KQkq - 0 5",
    "idea": "Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Petrov's Defense: French Attack is identified by the canonical ECO C42 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Petrov's Defense: French Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nxe5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxe5 from f3 to e5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from e5 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "player",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Use the Petrov's Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-petrov-s-defense-french-attack-8j0gy-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Petrov's%20Defense%3A%20French%20Attack%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Petrov's Defense: French Attack video lesson"
    }
  },
  {
    "id": "white-french-defense-hoffmann-gambit-1hfou",
    "name": "French Defense: Hoffmann Gambit",
    "side": "White",
    "tier": "free",
    "eco": "C00",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkbnr/ppp2ppp/8/3p4/3PPp2/8/PPP1Q1PP/RNB1KBNR w KQkq - 0 5",
    "idea": "Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "French Defense: Hoffmann Gambit is identified by the canonical ECO C00 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Hoffmann Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Qe2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Qe2 from d1 to e2. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e6 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "f4",
        "color": "white",
        "role": "player",
        "explanation": "White plays f4 from f2 to f4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "exf4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exf4 from e5 to f4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In French Defense: Hoffmann Gambit, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-french-defense-hoffmann-gambit-1hfou-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Hoffmann%20Gambit%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Defense: Hoffmann Gambit video lesson"
    }
  },
  {
    "id": "white-french-defense-advance-variation-1gnxf",
    "name": "French Defense: Advance Variation",
    "side": "White",
    "tier": "free",
    "eco": "C02",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkbnr/pp3ppp/2n1p3/2ppP3/3P4/2P5/PP3PPP/RNBQKBNR w KQkq - 1 5",
    "idea": "Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "French Defense: Advance Variation is identified by the canonical ECO C02 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Advance Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "e5",
        "color": "white",
        "role": "player",
        "explanation": "White plays e5 from e4 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "c3",
        "color": "white",
        "role": "player",
        "explanation": "White plays c3 from c2 to c3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Advance Variation, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-french-defense-advance-variation-1gnxf-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Advance%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable French Defense: Advance Variation video lesson"
    }
  },
  {
    "id": "white-french-defense-alekhine-chatard-attack-doj6o",
    "name": "French Defense: Alekhine-Chatard Attack",
    "side": "White",
    "tier": "free",
    "eco": "C13",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/pppnbppp/4p3/3pP1B1/3P3P/2N5/PPP2PP1/R2QKBNR b KQkq - 0 6",
    "idea": "Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "French Defense: Alekhine-Chatard Attack is identified by the canonical ECO C13 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Alekhine-Chatard Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e5",
        "color": "white",
        "role": "player",
        "explanation": "White plays e5 from e4 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Nfd7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nfd7 from f6 to d7. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "h4",
        "color": "white",
        "role": "player",
        "explanation": "White plays h4 from h2 to h4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Use the French Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-french-defense-alekhine-chatard-attack-doj6o-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Alekhine-Chatard%20Attack%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable French Defense: Alekhine-Chatard Attack video lesson"
    }
  },
  {
    "id": "white-caro-kann-defense-panov-attack-1qa71",
    "name": "Caro-Kann Defense: Panov Attack",
    "side": "White",
    "tier": "free",
    "eco": "B14",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/3p4/2PP4/2N5/PP3PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Caro-Kann Defense: Panov Attack is identified by the canonical ECO B14 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Panov Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "exd5",
        "color": "white",
        "role": "player",
        "explanation": "White plays exd5 from e4 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays cxd5 from c6 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "e6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-caro-kann-defense-panov-attack-1qa71-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Panov%20Attack%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Panov Attack video lesson"
    }
  },
  {
    "id": "white-caro-kann-defense-alien-gambit-xrppa",
    "name": "Caro-Kann Defense: Alien Gambit",
    "side": "White",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp2pNp1/2p2n1p/8/3P4/8/PPP2PPP/R1BQKBNR b KQkq - 0 6",
    "idea": "Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Caro-Kann Defense: Alien Gambit is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Alien Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Ng5",
        "color": "white",
        "role": "player",
        "explanation": "White plays Ng5 from e4 to g5. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "h6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays h6 from h7 to h6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "Nxf7",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxf7 from g5 to f7. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-caro-kann-defense-alien-gambit-xrppa-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Alien%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Alien Gambit video lesson"
    }
  },
  {
    "id": "white-caro-kann-defense-tartakower-variation-6alby",
    "name": "Caro-Kann Defense: Tartakower Variation",
    "side": "White",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/2p2p2/8/3P4/8/PPP2PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Caro-Kann Defense: Tartakower Variation is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Tartakower Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nxf6+",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxf6+ from e4 to f6. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "exf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays exf6 from e7 to f6. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-caro-kann-defense-tartakower-variation-6alby-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Tartakower%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Tartakower Variation video lesson"
    }
  },
  {
    "id": "white-caro-kann-defense-alekhine-gambit-103k6",
    "name": "Caro-Kann Defense: Alekhine Gambit",
    "side": "White",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp2pppp/2p2n2/8/3PN3/3B4/PPP2PPP/R1BQK1NR b KQkq - 2 5",
    "idea": "Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Caro-Kann Defense: Alekhine Gambit is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Alekhine Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bd3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bd3 from f1 to d3. The move activates a bishop on a diagonal that influences the center or the enemy king. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-caro-kann-defense-alekhine-gambit-103k6-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Alekhine%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Alekhine Gambit video lesson"
    }
  },
  {
    "id": "white-caro-kann-defense-1sbxl",
    "name": "Caro-Kann Defense",
    "side": "White",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "rnbqkbnr/pp2pppp/2p5/8/3Pp3/2N5/PPP2PPP/R1BQKBNR w KQkq - 0 4",
    "idea": "Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Caro-Kann Defense is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense, relate it to this course objective: Use the Caro-Kann Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-caro-kann-defense-1sbxl-branch-1",
        "opponentMove": "1...c5",
        "answer": "Bc4",
        "explanation": "Bc4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Caro-Kann Defense video lesson"
    }
  },
  {
    "id": "white-king-s-indian-attack-french-variation-12g2n",
    "name": "King's Indian Attack: French Variation",
    "side": "White",
    "tier": "free",
    "eco": "A08",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "r1bqkbnr/pp2pppp/2n5/2pp4/8/5NP1/PPPPPPBP/RNBQK2R w KQkq - 2 4",
    "idea": "Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "King's Indian Attack: French Variation is identified by the canonical ECO A08 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: French Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: French Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: French Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: French Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: French Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: French Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nc6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: French Variation, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-king-s-indian-attack-french-variation-12g2n-branch-1",
        "opponentMove": "1...c5",
        "answer": "Nd4",
        "explanation": "Nd4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20French%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack: French Variation video lesson"
    }
  },
  {
    "id": "white-king-s-indian-attack-with-bf5-jtqla",
    "name": "King's Indian Attack, with Bf5",
    "side": "White",
    "tier": "free",
    "eco": "A07",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rn1qkb1r/pp2ppp1/2p2n1p/3p1b2/8/3P1NP1/PPP1PPBP/RNBQ1RK1 w kq - 0 6",
    "idea": "Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "King's Indian Attack, with Bf5 is identified by the canonical ECO A07 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack, with Bf5 as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bf5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bf5 from c8 to f5. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "player",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "h6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays h6 from h7 to h6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-king-s-indian-attack-with-bf5-jtqla-branch-1",
        "opponentMove": "1...c5",
        "answer": "Nd4",
        "explanation": "Nd4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%2C%20with%20Bf5%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack, with Bf5 video lesson"
    }
  },
  {
    "id": "white-king-s-indian-attack-wahls-defense-9tpze",
    "name": "King's Indian Attack: Wahls Defense",
    "side": "White",
    "tier": "free",
    "eco": "A05",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbq1rk1/ppp1ppbp/5np1/3p4/8/3P1NP1/PPP1PPBP/RNBQ1RK1 w - - 0 6",
    "idea": "Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "King's Indian Attack: Wahls Defense is identified by the canonical ECO A05 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: Wahls Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "player",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "player",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "player",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "O-O",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays O-O from e8 to g8. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "player",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Use the King's Indian Attack move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-king-s-indian-attack-wahls-defense-9tpze-branch-1",
        "opponentMove": "1...c5",
        "answer": "Nd4",
        "explanation": "Nd4 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20Wahls%20Defense%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable King's Indian Attack: Wahls Defense video lesson"
    }
  },
  {
    "id": "white-benoni-defense-king-s-indian-system-10ljn",
    "name": "Benoni Defense: King's Indian System",
    "side": "White",
    "tier": "free",
    "eco": "A56",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3p1p/3p1np1/2pPp3/2P1P3/2N5/PP3PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Complete development, make the king safe, identify the thematic central break, and use the pawn structure to choose the correct wing for play.",
    "whyLearn": "Benoni Defense: King's Indian System is identified by the canonical ECO A56 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Benoni Defense: King's Indian System as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "player",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "player",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d5",
        "color": "white",
        "role": "player",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "e5",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "player",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "d6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "player",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "opponent",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Use the Benoni Defense move order to claim useful central influence, develop with purpose, and reach a position whose plans can be understood rather than guessed. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "white-benoni-defense-king-s-indian-system-10ljn-branch-1",
        "opponentMove": "1...c5",
        "answer": "dxc5",
        "explanation": "dxc5 is a legal, practical reply to c5: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Benoni%20Defense%3A%20King's%20Indian%20System%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Benoni Defense: King's Indian System video lesson"
    }
  },
  {
    "id": "caro-kann",
    "name": "Caro–Kann Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rn1qkbnr/pp2pppp/2p5/5b2/3PN3/8/PPP2PPP/R1BQKBNR w KQkq - 1 5",
    "idea": "Challenge e4 with ...d5 while keeping the light bishop outside the pawn chain.",
    "structure": "Solid center with a healthy c-pawn",
    "plan": "Develop the light bishop, play ...e6, and finish development before counterattacking.",
    "whyLearn": "Caro–Kann Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Playing ...e6 too early and trapping the c8 bishop."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6. This improves coordination and prepares the next stage of the opening. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxe4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bf5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bf5. This activates a bishop on a diagonal that supports the opening's central plan. In the Caro–Kann Defense, connect it to the main idea: challenge e4 with ...d5 while keeping the light bishop outside the pawn chain. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "caro-kann-branch-1",
        "opponentMove": "2.d4",
        "answer": "d5",
        "explanation": "d5 challenges the full center immediately. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Caro%E2%80%93Kann%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Caro–Kann Defense video lesson"
    }
  },
  {
    "id": "queens-gambit-declined",
    "name": "Queen's Gambit Declined",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 56,
    "simplicity": 5,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/3p2B1/2PP4/2N5/PP2PPPP/R2QKBNR w KQkq - 4 5",
    "idea": "Hold d5 with e6 and develop a compact, classical position.",
    "structure": "Tense d5 center with a closed light bishop",
    "plan": "Develop Nf6 and Be7, castle, then use ...c5 or ...e5 to free the position.",
    "whyLearn": "Queen's Gambit Declined gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Staying cramped without preparing a freeing pawn break."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg5. This activates a bishop on a diagonal that supports the opening's central plan. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be7. This activates a bishop on a diagonal that supports the opening's central plan. In the Queen's Gambit Declined, connect it to the main idea: hold d5 with e6 and develop a compact, classical position. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "queens-gambit-declined-branch-1",
        "opponentMove": "2.c4",
        "answer": "e6",
        "explanation": "e6 reinforces d5. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Queen's Gambit Declined video lesson"
    }
  },
  {
    "id": "kings-indian",
    "name": "King's Indian Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Advanced",
    "benchmark": 56,
    "simplicity": 2,
    "explorerFen": "rnbqk2r/ppp1ppbp/3p1np1/8/2PPP3/2N5/PP3PPP/R1BQKBNR w KQkq - 0 5",
    "idea": "Allow White space, then attack the center with ...e5 or ...c5.",
    "structure": "Closed center with opposite-wing play",
    "plan": "Fianchetto, castle, strike the center, and attack only on the wing dictated by the pawn chain.",
    "whyLearn": "King's Indian Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Starting a kingside pawn storm before closing the center."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the King's Indian Defense, connect it to the main idea: allow White space, then attack the center with ...e5 or ...c5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "kings-indian-branch-1",
        "opponentMove": "2.c4",
        "answer": "g6",
        "explanation": "g6 prepares the fianchetto. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable King's Indian Defense video lesson"
    }
  },
  {
    "id": "sicilian-najdorf",
    "name": "Sicilian Najdorf",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Advanced",
    "benchmark": 49,
    "simplicity": 2,
    "explorerFen": "rnbqkb1r/1p2pppp/p2p1n2/8/3NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 0 6",
    "idea": "Create an asymmetric fight and use ...a6 to control b5 before queenside expansion.",
    "structure": "Open c-file with unequal pawn majorities",
    "plan": "Develop quickly, choose ...e5 or ...e6, and never grab pawns while behind in development.",
    "whyLearn": "Sicilian Najdorf gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Memorizing ...a6 without knowing which central break follows."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 9,
        "san": "a6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays a6. This improves coordination and prepares the next stage of the opening. In the Sicilian Najdorf, connect it to the main idea: create an asymmetric fight and use ...a6 to control b5 before queenside expansion. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "sicilian-najdorf-branch-1",
        "opponentMove": "2.Nf3",
        "answer": "d6",
        "explanation": "d6 controls e5 and prepares Nf6. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Najdorf%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Sicilian Najdorf video lesson"
    }
  },
  {
    "id": "accelerated-dragon",
    "name": "Accelerated Dragon",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "r1bqkbnr/pp1ppp1p/2n3p1/8/3NP3/8/PPP2PPP/RNBQKB1R w KQkq - 0 5",
    "idea": "Fianchetto quickly and keep the option of an immediate ...d5 break.",
    "structure": "Open Sicilian with a powerful g7 bishop",
    "plan": "Develop Bg7, look for ...d5 in one move, and know the Maroczy Bind plan.",
    "whyLearn": "Accelerated Dragon gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Playing a slow ...d6 and losing the point of acceleration."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Accelerated Dragon, connect it to the main idea: fianchetto quickly and keep the option of an immediate ...d5 break. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "accelerated-dragon-branch-1",
        "opponentMove": "2.Nf3",
        "answer": "Nc6",
        "explanation": "Nc6 develops and watches d4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Accelerated%20Dragon%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Accelerated Dragon video lesson"
    }
  },
  {
    "id": "classical-sicilian",
    "name": "Classical Sicilian",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "r1bqkb1r/pp2pppp/2np1n2/8/3NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 0 6",
    "idea": "Use both knights actively before choosing the final pawn structure.",
    "structure": "Open Sicilian with flexible central control",
    "plan": "Develop Nc6/Nf6, play ...d6, and choose ...e5 or ...e6 based on White's setup.",
    "whyLearn": "Classical Sicilian gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Allowing e5 with tempo on f6 without calculating."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 9,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Classical Sicilian, connect it to the main idea: use both knights actively before choosing the final pawn structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "classical-sicilian-branch-1",
        "opponentMove": "2.Nf3",
        "answer": "Nc6",
        "explanation": "Nc6 develops toward d4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Classical%20Sicilian%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Classical Sicilian video lesson"
    }
  },
  {
    "id": "french-defense",
    "name": "French Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqkb1r/pppn1ppp/4p3/3pP3/3P4/2N5/PPP2PPP/R1BQKBNR w KQkq - 1 5",
    "idea": "Attack e4 with ...d5 and counter White's space at its base.",
    "structure": "Locked pawn chain with c5 and f6 breaks",
    "plan": "Play ...c5 quickly, pressure d4, and free the c8 bishop later through structure changes.",
    "whyLearn": "French Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Attacking e5 directly while ignoring d4."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "e5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e5. This improves coordination and prepares the next stage of the opening. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nfd7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nfd7. This develops a knight toward useful central squares while adding control over key pawn breaks. In the French Defense, connect it to the main idea: attack e4 with ...d5 and counter White's space at its base. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "french-defense-branch-1",
        "opponentMove": "2.d4",
        "answer": "d5",
        "explanation": "d5 challenges the center. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Defense video lesson"
    }
  },
  {
    "id": "scandinavian-defense",
    "name": "Scandinavian Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkbnr/ppp1pppp/8/8/8/2N5/PPPP1PPP/R1BQKBNR w KQkq - 2 4",
    "idea": "Challenge e4 immediately and accept a queen tempo for a clear structure.",
    "structure": "Open center with straightforward development",
    "plan": "Retreat the queen safely, develop Bf5/Bg4, and avoid repeated queen moves.",
    "whyLearn": "Scandinavian Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Trying to punish every knight attack with another queen adventure."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Scandinavian Defense, connect it to the main idea: challenge e4 immediately and accept a queen tempo for a clear structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Scandinavian Defense, connect it to the main idea: challenge e4 immediately and accept a queen tempo for a clear structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "exd5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays exd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Scandinavian Defense, connect it to the main idea: challenge e4 immediately and accept a queen tempo for a clear structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Qxd5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Scandinavian Defense, connect it to the main idea: challenge e4 immediately and accept a queen tempo for a clear structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Scandinavian Defense, connect it to the main idea: challenge e4 immediately and accept a queen tempo for a clear structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Qd8",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qd8. This places the queen where it supports a concrete threat; early queen moves should always have this specific justification. In the Scandinavian Defense, connect it to the main idea: challenge e4 immediately and accept a queen tempo for a clear structure. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "scandinavian-defense-branch-1",
        "opponentMove": "2.exd5",
        "answer": "Qxd5",
        "explanation": "Qxd5 restores material immediately. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Scandinavian%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Scandinavian Defense video lesson"
    }
  },
  {
    "id": "alekhines-defense",
    "name": "Alekhine Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 50,
    "simplicity": 4,
    "explorerFen": "rnbqkb1r/ppp1pppp/3p4/3nP3/3P4/5N2/PPP2PPP/RNBQKB1R b KQkq - 1 4",
    "idea": "Provoke White's pawns forward, then attack the extended center.",
    "structure": "Advanced white center targeted by pawn breaks",
    "plan": "Use ...d6 and ...c5, develop, and attack the pawn chain rather than the king too early.",
    "whyLearn": "Alekhine Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Moving the knight repeatedly without creating central counterplay."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "e5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e5. This improves coordination and prepares the next stage of the opening. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nd5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nd5. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Alekhine Defense, connect it to the main idea: provoke White's pawns forward, then attack the extended center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "alekhines-defense-branch-1",
        "opponentMove": "2.e5",
        "answer": "Nd5",
        "explanation": "Nd5 invites the pawns forward. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Alekhine%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Alekhine Defense video lesson"
    }
  },
  {
    "id": "pirc-defense",
    "name": "Pirc Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqk2r/ppp1ppbp/3p1np1/8/3PPP2/2N5/PPP3PP/R1BQKBNR w KQkq - 1 5",
    "idea": "Let White build a center, then undermine it with pieces and pawn breaks.",
    "structure": "Broad white center versus a compact fianchetto",
    "plan": "Castle quickly, choose ...e5 or ...c5, and challenge the center before it rolls forward.",
    "whyLearn": "Pirc Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Waiting too long to strike the center."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "f4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the Pirc Defense, connect it to the main idea: let White build a center, then undermine it with pieces and pawn breaks. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "pirc-defense-branch-1",
        "opponentMove": "2.d4",
        "answer": "Nf6",
        "explanation": "Nf6 attacks e4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Pirc%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Pirc Defense video lesson"
    }
  },
  {
    "id": "modern-defense",
    "name": "Modern Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqk1nr/ppp1ppbp/3p2p1/8/3PPP2/2N5/PPP3PP/R1BQKBNR b KQkq - 0 4",
    "idea": "Stay flexible with a fianchetto and delay the king knight's commitment.",
    "structure": "Hypermodern pressure on a broad center",
    "plan": "Develop Bg7, choose ...d6 and ...c5/e5, and react to White's exact setup.",
    "whyLearn": "Modern Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Being so flexible that no central break is ever played."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "f4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays f4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Modern Defense, connect it to the main idea: stay flexible with a fianchetto and delay the king knight's commitment. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "modern-defense-branch-1",
        "opponentMove": "2.d4",
        "answer": "Bg7",
        "explanation": "Bg7 immediately targets the long diagonal. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Modern%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Modern Defense video lesson"
    }
  },
  {
    "id": "petroff-defense",
    "name": "Petroff Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkb1r/ppp2ppp/3p4/8/4n3/5N2/PPPP1PPP/RNBQKB1R w KQkq - 0 5",
    "idea": "Counterattack e4 instead of passively defending e5.",
    "structure": "Symmetrical open center with tactical early exchanges",
    "plan": "Know the Nxe5 sequence, develop calmly, and use equality to create later imbalances.",
    "whyLearn": "Petroff Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Copying White's moves one move too far in tactical positions."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nxe5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nxe4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Petroff Defense, connect it to the main idea: counterattack e4 instead of passively defending e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "petroff-defense-branch-1",
        "opponentMove": "2.Nf3",
        "answer": "Nf6",
        "explanation": "Nf6 counterattacks e4. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Petroff%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Petroff Defense video lesson"
    }
  },
  {
    "id": "berlin-defense",
    "name": "Berlin Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "r1bqkb1r/pppp1ppp/2n5/1B2p3/4n3/5N2/PPPP1PPP/RNBQ1RK1 w kq - 0 5",
    "idea": "Challenge e4 immediately in the Ruy Lopez and offer a resilient endgame.",
    "structure": "Open center or queenless Berlin structure",
    "plan": "Develop naturally, understand the e4 tactic, and value activity over keeping every pawn.",
    "whyLearn": "Berlin Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Taking e4 without checking whether d4 wins the knight."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb5. This activates a bishop on a diagonal that supports the opening's central plan. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O. This moves the king out of the center and connects a rook, so the next central break is safer. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nxe4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Berlin Defense, connect it to the main idea: challenge e4 immediately in the Ruy Lopez and offer a resilient endgame. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "berlin-defense-branch-1",
        "opponentMove": "3.Bb5",
        "answer": "Nf6",
        "explanation": "Nf6 attacks e4 and refuses passivity. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Berlin%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Berlin Defense video lesson"
    }
  },
  {
    "id": "philidor-defense",
    "name": "Philidor Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "r1bqkb1r/pppn1ppp/3p1n2/4p3/3PP3/2N2N2/PPP2PPP/R1BQKB1R w KQkq - 3 5",
    "idea": "Support e5 solidly and develop into a compact center.",
    "structure": "Closed e5/d6 shell",
    "plan": "Develop Nf6/Nbd7, Be7 and castle, then seek ...c6 and ...Qc7 or ...d5.",
    "whyLearn": "Philidor Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Blocking every piece and never playing a freeing break."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nbd7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nbd7. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Philidor Defense, connect it to the main idea: support e5 solidly and develop into a compact center. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "philidor-defense-branch-1",
        "opponentMove": "2.Nf3",
        "answer": "d6",
        "explanation": "d6 reinforces e5. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Philidor%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Philidor Defense video lesson"
    }
  },
  {
    "id": "slav-defense",
    "name": "Slav Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkb1r/pp2pppp/2p2n2/8/2pP4/2N2N2/PP2PPPP/R1BQKB1R w KQkq - 0 5",
    "idea": "Support d5 with the c-pawn while keeping the light bishop free.",
    "structure": "Solid d5/c6 triangle",
    "plan": "Develop Nf6/Bf5, decide when to take c4, and use ...b5 only when it is sustainable.",
    "whyLearn": "Slav Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Holding the c4 pawn at the cost of development."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6. This improves coordination and prepares the next stage of the opening. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "dxc4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc4. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Slav Defense, connect it to the main idea: support d5 with the c-pawn while keeping the light bishop free. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "slav-defense-branch-1",
        "opponentMove": "2.c4",
        "answer": "c6",
        "explanation": "c6 reinforces d5. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Slav%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Slav Defense video lesson"
    }
  },
  {
    "id": "semi-slav",
    "name": "Semi-Slav Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 5,
    "explorerFen": "rnbqkb1r/pp3ppp/2p1pn2/3p4/2PP4/2N2N2/PP2PPPP/R1BQKB1R w KQkq - 0 5",
    "idea": "Combine QGD solidity with Slav support for d5.",
    "structure": "Compact d5/e6/c6 triangle",
    "plan": "Develop carefully, choose ...dxc4 or ...Nbd7, and prepare ...e5 or ...c5.",
    "whyLearn": "Semi-Slav Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Locking in both bishops without a plan to free them."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6. This improves coordination and prepares the next stage of the opening. In the Semi-Slav Defense, connect it to the main idea: combine QGD solidity with Slav support for d5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "semi-slav-branch-1",
        "opponentMove": "2.c4",
        "answer": "e6",
        "explanation": "e6 holds d5. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Semi-Slav%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Semi-Slav Defense video lesson"
    }
  },
  {
    "id": "nimzo-indian",
    "name": "Nimzo–Indian Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbq1rk1/pppp1ppp/4pn2/8/1bPP4/2N1P3/PP3PPP/R1BQKBNR w KQ - 1 5",
    "idea": "Pin the c3 knight and fight e4 without occupying the center with pawns.",
    "structure": "Flexible center with potential doubled c-pawns",
    "plan": "Castle, choose pressure on c3 or d4, and trade the bishop only for a structural reason.",
    "whyLearn": "Nimzo–Indian Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Giving up the dark bishop without gaining structure or time."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Bb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bb4. This activates a bishop on a diagonal that supports the opening's central plan. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "O-O",
        "color": "black",
        "role": "player",
        "explanation": "Black plays O-O. This moves the king out of the center and connects a rook, so the next central break is safer. In the Nimzo–Indian Defense, connect it to the main idea: pin the c3 knight and fight e4 without occupying the center with pawns. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "nimzo-indian-branch-1",
        "opponentMove": "2.c4",
        "answer": "e6",
        "explanation": "e6 controls d5 and opens the bishop. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Nimzo%E2%80%93Indian%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Nimzo–Indian Defense video lesson"
    }
  },
  {
    "id": "queens-indian",
    "name": "Queen's Indian Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 56,
    "simplicity": 4,
    "explorerFen": "rn1qkb1r/p1pp1ppp/bp2pn2/8/2PP4/5NP1/PP2PP1P/RNBQKB1R w KQkq - 1 5",
    "idea": "Control e4 with pieces and develop the queen bishop actively.",
    "structure": "Flexible queenside fianchetto",
    "plan": "Use ...Bb7 or ...Ba6, develop Be7, castle, and strike with ...c5 or ...d5.",
    "whyLearn": "Queen's Indian Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Making queenside bishop moves while neglecting the king."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "b6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays b6. This improves coordination and prepares the next stage of the opening. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Ba6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ba6. This activates a bishop on a diagonal that supports the opening's central plan. In the Queen's Indian Defense, connect it to the main idea: control e4 with pieces and develop the queen bishop actively. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "queens-indian-branch-1",
        "opponentMove": "2.c4",
        "answer": "e6",
        "explanation": "e6 controls d5 and opens the bishop. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Indian%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Queen's Indian Defense video lesson"
    }
  },
  {
    "id": "grunfeld-defense",
    "name": "Grünfeld Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Advanced",
    "benchmark": 49,
    "simplicity": 2,
    "explorerFen": "rnbqkb1r/ppp1pp1p/6p1/3n4/3PP3/2N5/PP3PPP/R1BQKBNR b KQkq - 0 5",
    "idea": "Let White build a pawn center, then attack it immediately with pieces.",
    "structure": "Large white center under direct pressure",
    "plan": "Use Bg7, c5 and Nc6 to attack d4; trade the center before it can advance.",
    "whyLearn": "Grünfeld Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Admiring White's center instead of attacking it."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5. This improves coordination and prepares the next stage of the opening. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "cxd5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays cxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Nxd5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Grünfeld Defense, connect it to the main idea: let White build a pawn center, then attack it immediately with pieces. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "grunfeld-defense-branch-1",
        "opponentMove": "3.Nc3",
        "answer": "d5",
        "explanation": "d5 strikes before White consolidates. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Gr%C3%BCnfeld%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Grünfeld Defense video lesson"
    }
  },
  {
    "id": "dutch-defense",
    "name": "Dutch Defense",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqk2r/ppppp1bp/5np1/5p2/3P4/5NP1/PPP1PPBP/RNBQK2R w KQkq - 2 5",
    "idea": "Control e4 and build kingside space from move one.",
    "structure": "Stonewall, Leningrad, or Classical kingside structure",
    "plan": "Develop Nf6 and Bg7/e7, castle, then choose ...d6/e5 or a Stonewall setup.",
    "whyLearn": "Dutch Defense gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Pushing kingside pawns while leaving the king in the center."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "f5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays f5. This improves coordination and prepares the next stage of the opening. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2. This activates a bishop on a diagonal that supports the opening's central plan. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6. This improves coordination and prepares the next stage of the opening. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7. This activates a bishop on a diagonal that supports the opening's central plan. In the Dutch Defense, connect it to the main idea: control e4 and build kingside space from move one. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "dutch-defense-branch-1",
        "opponentMove": "2.g3",
        "answer": "Nf6",
        "explanation": "Nf6 controls e4 and develops. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Dutch%20Defense%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Dutch Defense video lesson"
    }
  },
  {
    "id": "modern-benoni",
    "name": "Modern Benoni",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Advanced",
    "benchmark": 49,
    "simplicity": 2,
    "explorerFen": "rnbqkb1r/pp3ppp/3p1n2/2pP4/8/2N5/PP2PPPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Invite d5, then undermine it with ...e6 and queenside play.",
    "structure": "Asymmetric pawn majorities and an open e-file",
    "plan": "Use Bg7, castle, seek ...b5, and pressure e4 while respecting White's central space.",
    "whyLearn": "Modern Benoni gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Playing ...b5 before development makes it tactically sound."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5. This improves coordination and prepares the next stage of the opening. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "d5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d5. This improves coordination and prepares the next stage of the opening. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6. This improves coordination and prepares the next stage of the opening. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 7,
        "san": "exd5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays exd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 8,
        "san": "cxd5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays cxd5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 9,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6. This improves coordination and prepares the next stage of the opening. In the Modern Benoni, connect it to the main idea: invite d5, then undermine it with ...e6 and queenside play. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "modern-benoni-branch-1",
        "opponentMove": "3.d5",
        "answer": "e6",
        "explanation": "e6 attacks the advanced chain. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Modern%20Benoni%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Modern Benoni video lesson"
    }
  },
  {
    "id": "budapest-gambit",
    "name": "Budapest Gambit",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "benchmark": 49,
    "simplicity": 4,
    "explorerFen": "rnbqkb1r/pppp1ppp/8/4P3/2P3n1/8/PP2PPPP/RNBQKBNR w KQkq - 1 4",
    "idea": "Offer a pawn to gain rapid development and pressure e5.",
    "structure": "Open lines with a temporary pawn sacrifice",
    "plan": "Attack e5 with Ng4/Nc6, develop Bc5, and recover the pawn without queen adventures.",
    "whyLearn": "Budapest Gambit gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Forcing pawn recovery when development is the real compensation."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Budapest Gambit, connect it to the main idea: offer a pawn to gain rapid development and pressure e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Budapest Gambit, connect it to the main idea: offer a pawn to gain rapid development and pressure e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Budapest Gambit, connect it to the main idea: offer a pawn to gain rapid development and pressure e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Budapest Gambit, connect it to the main idea: offer a pawn to gain rapid development and pressure e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "dxe5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays dxe5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Budapest Gambit, connect it to the main idea: offer a pawn to gain rapid development and pressure e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Ng4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ng4. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Budapest Gambit, connect it to the main idea: offer a pawn to gain rapid development and pressure e5. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "budapest-gambit-branch-1",
        "opponentMove": "2.c4",
        "answer": "e5",
        "explanation": "e5 immediately challenges White's center. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Budapest%20Gambit%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Budapest Gambit video lesson"
    }
  },
  {
    "id": "englund-gambit",
    "name": "Englund Gambit",
    "side": "Black",
    "tier": "free",
    "eco": null,
    "source": {
      "name": "Repertoire /64 curriculum",
      "license": "Original educational text"
    },
    "responseTo": "d4",
    "complexity": "Advanced",
    "benchmark": 49,
    "simplicity": 2,
    "explorerFen": "r1b1kbnr/ppppqppp/2n5/4P3/8/5N2/PPP1PPPP/RNBQKB1R w KQkq - 3 4",
    "idea": "Create an immediate tactical game against 1.d4.",
    "structure": "Open center with a sacrificed e-pawn",
    "plan": "Develop with threats, recover e5 only if safe, and accept that sound defense favors White.",
    "whyLearn": "Englund Gambit gives a beginner a clear map from move one: where the pieces belong, which pawn break matters, and how to react when the opponent refuses the main line.",
    "mistakes": [
      "Relying on one trap after White has avoided it."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4. This changes the pawn structure, claims space, and defines which pieces will have useful squares. In the Englund Gambit, connect it to the main idea: create an immediate tactical game against 1.d4. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5. This improves coordination and prepares the next stage of the opening. In the Englund Gambit, connect it to the main idea: create an immediate tactical game against 1.d4. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 2,
        "san": "dxe5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays dxe5. This clarifies a central tension or removes a defender; the point is the position gained after the exchange, not simply the captured material. In the Englund Gambit, connect it to the main idea: create an immediate tactical game against 1.d4. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Englund Gambit, connect it to the main idea: create an immediate tactical game against 1.d4. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3. This develops a knight toward useful central squares while adding control over key pawn breaks. In the Englund Gambit, connect it to the main idea: create an immediate tactical game against 1.d4. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      },
      {
        "ply": 5,
        "san": "Qe7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qe7. This places the queen where it supports a concrete threat; early queen moves should always have this specific justification. In the Englund Gambit, connect it to the main idea: create an immediate tactical game against 1.d4. Do not memorize the move alone—check the center, king safety, and your opponent's threat before repeating it."
      }
    ],
    "branches": [
      {
        "id": "englund-gambit-branch-1",
        "opponentMove": "2.dxe5",
        "answer": "Nc6",
        "explanation": "Nc6 develops while attacking e5. The practical rule is to answer the opponent's idea, then return to development and king safety."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Englund%20Gambit%20beginner%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Englund Gambit video lesson"
    }
  },
  {
    "id": "black-sicilian-defense-closed-1smlk",
    "name": "Sicilian Defense: Closed",
    "side": "Black",
    "tier": "free",
    "eco": "B25",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk1nr/pp2ppbp/2np2p1/2p5/4P3/2NP2P1/PPP2PBP/R1BQK1NR w KQkq - 0 6",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Sicilian Defense.",
    "whyLearn": "Sicilian Defense: Closed is identified by the canonical ECO B25 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Closed as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Closed, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-sicilian-defense-closed-1smlk-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Closed%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Closed video lesson"
    }
  },
  {
    "id": "black-sicilian-defense-pin-variation-1n5wl",
    "name": "Sicilian Defense: Pin Variation",
    "side": "Black",
    "tier": "free",
    "eco": "B40",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/pp1p1ppp/4pn2/8/1b1NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 3 6",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Sicilian Defense.",
    "whyLearn": "Sicilian Defense: Pin Variation is identified by the canonical ECO B40 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Pin Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Sicilian Defense: Pin Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-sicilian-defense-pin-variation-1n5wl-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Pin%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Pin Variation video lesson"
    }
  },
  {
    "id": "black-sicilian-defense-dragon-variation-14wp7",
    "name": "Sicilian Defense: Dragon Variation",
    "side": "Black",
    "tier": "free",
    "eco": "B70",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp2pp1p/3p1np1/8/3NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 0 6",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Sicilian Defense.",
    "whyLearn": "Sicilian Defense: Dragon Variation is identified by the canonical ECO B70 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Dragon Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Dragon Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-sicilian-defense-dragon-variation-14wp7-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Dragon%20Variation%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Sicilian Defense: Dragon Variation video lesson"
    }
  },
  {
    "id": "black-sicilian-defense-open-s4tng",
    "name": "Sicilian Defense: Open",
    "side": "Black",
    "tier": "free",
    "eco": "B33",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pp1ppppp/2n2n2/8/3NP3/8/PPP2PPP/RNBQKB1R w KQkq - 1 5",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Sicilian Defense.",
    "whyLearn": "Sicilian Defense: Open is identified by the canonical ECO B33 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Open as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Open, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-sicilian-defense-open-s4tng-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Open%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Open video lesson"
    }
  },
  {
    "id": "black-sicilian-defense-gaw-paw-variation-1kgdf",
    "name": "Sicilian Defense: Gaw-Paw Variation",
    "side": "Black",
    "tier": "free",
    "eco": "B40",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1kb1r/pp1p1ppp/1q2pn2/8/3NP3/2N5/PPP2PPP/R1BQKB1R w KQkq - 3 6",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Sicilian Defense.",
    "whyLearn": "Sicilian Defense: Gaw-Paw Variation is identified by the canonical ECO B40 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Sicilian Defense: Gaw-Paw Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Qb6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qb6 from d8 to b6. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Sicilian Defense: Gaw-Paw Variation, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Sicilian Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-sicilian-defense-gaw-paw-variation-1kgdf-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Sicilian%20Defense%3A%20Gaw-Paw%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Sicilian Defense: Gaw-Paw Variation video lesson"
    }
  },
  {
    "id": "black-pterodactyl-defense-sicilian-unpin-qdot2",
    "name": "Pterodactyl Defense: Sicilian, Unpin",
    "side": "Black",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1pppbp/6p1/q1p5/3PP3/2N2N2/PPPB1PPP/R2QKB1R b KQkq - 4 5",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Pterodactyl Defense.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Unpin is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Unpin as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bd2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bd2 from c1 to d2. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Unpin, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-pterodactyl-defense-sicilian-unpin-qdot2-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Unpin%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Unpin video lesson"
    }
  },
  {
    "id": "black-pterodactyl-defense-sicilian-quetzalcoatlus-1o5m2",
    "name": "Pterodactyl Defense: Sicilian, Quetzalcoatlus",
    "side": "Black",
    "tier": "free",
    "eco": "B06",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp2ppbp/3p2p1/q1p5/3PP3/2N2N2/PPP1BPPP/R1BQK2R w KQkq - 0 6",
    "idea": "Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Pterodactyl Defense.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Quetzalcoatlus is identified by the canonical ECO B06 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Quetzalcoatlus as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Be2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Be2 from f1 to e2. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Quetzalcoatlus, relate it to this course objective: Meet e4 with g6, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-pterodactyl-defense-sicilian-quetzalcoatlus-1o5m2-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Quetzalcoatlus%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Quetzalcoatlus video lesson"
    }
  },
  {
    "id": "black-king-s-indian-attack-sicilian-variation-2vyut",
    "name": "King's Indian Attack: Sicilian Variation",
    "side": "Black",
    "tier": "free",
    "eco": "A08",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/2pp4/8/3P1NP1/PPP1PPBP/RNBQ1RK1 b kq - 0 5",
    "idea": "Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the King's Indian Attack.",
    "whyLearn": "King's Indian Attack: Sicilian Variation is identified by the canonical ECO A08 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: Sicilian Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Sicilian Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-king-s-indian-attack-sicilian-variation-2vyut-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20Sicilian%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack: Sicilian Variation video lesson"
    }
  },
  {
    "id": "black-pterodactyl-defense-sicilian-anhanguera-qoyeb",
    "name": "Pterodactyl Defense: Sicilian, Anhanguera",
    "side": "Black",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1pppbp/6p1/q1p5/3PP3/2N1BN2/PPP2PPP/R2QKB1R b KQkq - 4 5",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Pterodactyl Defense.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Anhanguera is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Anhanguera as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Be3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Be3 from c1 to e3. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Anhanguera, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-pterodactyl-defense-sicilian-anhanguera-qoyeb-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Anhanguera%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Anhanguera video lesson"
    }
  },
  {
    "id": "black-pterodactyl-defense-sicilian-pteranodon-5zln0",
    "name": "Pterodactyl Defense: Sicilian, Pteranodon",
    "side": "Black",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1ppp1p/6p1/q1P5/4P3/2P2N2/P1P2PPP/R1BQKB1R b KQkq - 0 6",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Pterodactyl Defense.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Pteranodon is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Pteranodon as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "dxc5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays dxc5 from d4 to c5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5+",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qa5+ from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bxc3+",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bxc3+ from g7 to c3. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "bxc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays bxc3 from b2 to c3. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Pterodactyl Defense: Sicilian, Pteranodon, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-pterodactyl-defense-sicilian-pteranodon-5zln0-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Pteranodon%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Pteranodon video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-accepted-1rbiu",
    "name": "Queen's Gambit Accepted",
    "side": "Black",
    "tier": "free",
    "eco": "D24",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/ppp2ppp/4pn2/8/2pPP3/2N2N2/PP3PPP/R1BQKB1R b KQkq - 0 5",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Accepted.",
    "whyLearn": "Queen's Gambit Accepted is identified by the canonical ECO D24 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "dxc4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-accepted-1rbiu-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted video lesson"
    }
  },
  {
    "id": "black-pterodactyl-defense-sicilian-benoni-gambit-1d7h5",
    "name": "Pterodactyl Defense: Sicilian, Benoni Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "B27",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnb1k1nr/pp1pppbp/6p1/q1pP4/4P3/2N2N2/PPP2PPP/R1BQKB1R b KQkq - 0 5",
    "idea": "Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Pterodactyl Defense.",
    "whyLearn": "Pterodactyl Defense: Sicilian, Benoni Gambit is identified by the canonical ECO B27 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Pterodactyl Defense: Sicilian, Benoni Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Qa5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Qa5 from d8 to a5. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Pterodactyl Defense: Sicilian, Benoni Gambit, relate it to this course objective: Meet e4 with c5, challenge White's center, and develop into the recognizable Pterodactyl Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-pterodactyl-defense-sicilian-benoni-gambit-1d7h5-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Pterodactyl%20Defense%3A%20Sicilian%2C%20Benoni%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Pterodactyl Defense: Sicilian, Benoni Gambit video lesson"
    }
  },
  {
    "id": "black-van-geet-opening-sicilian-two-knights-100cm",
    "name": "Van Geet Opening: Sicilian Two Knights",
    "side": "Black",
    "tier": "free",
    "eco": "A00",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nc3",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "r1bqkbnr/pp1ppppp/2n5/8/3N4/2N5/PPP1PPPP/R1BQKB1R b KQkq - 0 4",
    "idea": "Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Van Geet Opening.",
    "whyLearn": "Van Geet Opening: Sicilian Two Knights is identified by the canonical ECO A00 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Van Geet Opening: Sicilian Two Knights as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd4 from c5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxd4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxd4 from f3 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Van Geet Opening: Sicilian Two Knights, relate it to this course objective: Meet Nc3 with c5, challenge White's center, and develop into the recognizable Van Geet Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-van-geet-opening-sicilian-two-knights-100cm-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Van%20Geet%20Opening%3A%20Sicilian%20Two%20Knights%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Van Geet Opening: Sicilian Two Knights video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-declined-lasker-defense-6oabe",
    "name": "Queen's Gambit Declined: Lasker Defense",
    "side": "Black",
    "tier": "free",
    "eco": "D53",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4p3/3p2B1/2PPn3/2N1P3/PP3PPP/R2QKBNR w KQkq - 1 6",
    "idea": "Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Declined.",
    "whyLearn": "Queen's Gambit Declined: Lasker Defense is identified by the canonical ECO D53 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Lasker Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Ne4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ne4 from f6 to e4. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Lasker Defense, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-declined-lasker-defense-6oabe-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Lasker%20Defense%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Queen's Gambit Declined: Lasker Defense video lesson"
    }
  },
  {
    "id": "black-benoni-defense-franco-sicilian-hybrid-1vos6",
    "name": "Benoni Defense: Franco-Sicilian Hybrid",
    "side": "Black",
    "tier": "free",
    "eco": "A40",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/pp2npbp/3p2p1/2pP4/4P3/2N2N2/PP3PPP/R1BQKB1R w KQkq - 3 8",
    "idea": "Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Benoni Defense.",
    "whyLearn": "Benoni Defense: Franco-Sicilian Hybrid is identified by the canonical ECO A40 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Benoni Defense: Franco-Sicilian Hybrid as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "exd5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays exd5 from e6 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "cxd5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays cxd5 from c4 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 11,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 12,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 13,
        "san": "Ne7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ne7 from g8 to e7. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: Franco-Sicilian Hybrid, relate it to this course objective: Meet d4 with e6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-benoni-defense-franco-sicilian-hybrid-1vos6-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Benoni%20Defense%3A%20Franco-Sicilian%20Hybrid%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Benoni Defense: Franco-Sicilian Hybrid video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-accepted-classical-defense-5dry0",
    "name": "Queen's Gambit Accepted: Classical Defense",
    "side": "Black",
    "tier": "free",
    "eco": "D26",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/2p5/2BP4/4PN2/PP3PPP/RNBQK2R w KQkq - 0 6",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Accepted.",
    "whyLearn": "Queen's Gambit Accepted: Classical Defense is identified by the canonical ECO D26 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Classical Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bxc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bxc4 from f1 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Classical Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-accepted-classical-defense-5dry0-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Classical%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Classical Defense video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-accepted-linares-variation-1octx",
    "name": "Queen's Gambit Accepted: Linares Variation",
    "side": "Black",
    "tier": "free",
    "eco": "D20",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/p3pppp/5n2/1ppP4/2p1P3/2N5/PP3PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Accepted.",
    "whyLearn": "Queen's Gambit Accepted: Linares Variation is identified by the canonical ECO D20 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Linares Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "d5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "b5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays b5 from b7 to b5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Linares Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-accepted-linares-variation-1octx-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Linares%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Linares Variation video lesson"
    }
  },
  {
    "id": "black-english-opening-mikenas-carls-sicilian-1xdtr",
    "name": "English Opening: Mikenas-Carls, Sicilian",
    "side": "Black",
    "tier": "free",
    "eco": "A19",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "c4",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp1p1ppp/4pn2/2p5/2P1P3/2N5/PP1P1PPP/R1BQKBNR w KQkq - 0 4",
    "idea": "Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the English Opening.",
    "whyLearn": "English Opening: Mikenas-Carls, Sicilian is identified by the canonical ECO A19 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name English Opening: Mikenas-Carls, Sicilian as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: Mikenas-Carls, Sicilian, relate it to this course objective: Meet c4 with e6, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-english-opening-mikenas-carls-sicilian-1xdtr-branch-1",
        "opponentMove": "1.d4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to d4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=English%20Opening%3A%20Mikenas-Carls%2C%20Sicilian%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable English Opening: Mikenas-Carls, Sicilian video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-declined-manhattan-variation-m4cz9",
    "name": "Queen's Gambit Declined: Manhattan Variation",
    "side": "Black",
    "tier": "free",
    "eco": "D51",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppn1ppp/4pn2/3p2B1/1bPP4/2N1P3/PP3PPP/R2QKBNR w KQkq - 1 6",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Declined.",
    "whyLearn": "Queen's Gambit Declined: Manhattan Variation is identified by the canonical ECO D51 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Manhattan Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nbd7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nbd7 from b8 to d7. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Manhattan Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-declined-manhattan-variation-m4cz9-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Manhattan%20Variation%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Queen's Gambit Declined: Manhattan Variation video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-declined-spielmann-variation-1naqd",
    "name": "Queen's Gambit Declined: Spielmann Variation",
    "side": "Black",
    "tier": "free",
    "eco": "D30",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3p1p/2p1pnp1/3p4/2PP4/4PN2/PP1N1PPP/R1BQKB1R w KQkq - 0 6",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Declined.",
    "whyLearn": "Queen's Gambit Declined: Spielmann Variation is identified by the canonical ECO D30 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Spielmann Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nbd2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nbd2 from b1 to d2. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Spielmann Variation, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-declined-spielmann-variation-1naqd-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Spielmann%20Variation%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Queen's Gambit Declined: Spielmann Variation video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-declined-harrwitz-attack-3hsn2",
    "name": "Queen's Gambit Declined: Harrwitz Attack",
    "side": "Black",
    "tier": "free",
    "eco": "D37",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/3p4/2PP1B2/2N2N2/PP2PPPP/R2QKB1R b KQkq - 3 5",
    "idea": "Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Declined.",
    "whyLearn": "Queen's Gambit Declined: Harrwitz Attack is identified by the canonical ECO D37 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Harrwitz Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bf4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bf4 from c1 to f4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Harrwitz Attack, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-declined-harrwitz-attack-3hsn2-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Harrwitz%20Attack%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Declined: Harrwitz Attack video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-declined-miles-variation-1g25k",
    "name": "Queen's Gambit Declined: Miles Variation",
    "side": "Black",
    "tier": "free",
    "eco": "D37",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbq1rk1/ppp1bppp/4pn2/3p2B1/2PP4/2N2N2/PPQ1PPPP/R3KB1R b KQ - 5 6",
    "idea": "Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Declined.",
    "whyLearn": "Queen's Gambit Declined: Miles Variation is identified by the canonical ECO D37 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Declined: Miles Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bg5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "O-O",
        "color": "black",
        "role": "player",
        "explanation": "Black plays O-O from e8 to g8. The move secures the king and connects the rooks before the center opens. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "Qc2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Qc2 from d1 to c2. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In Queen's Gambit Declined: Miles Variation, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Queen's Gambit Declined structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-declined-miles-variation-1g25k-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Declined%3A%20Miles%20Variation%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Queen's Gambit Declined: Miles Variation video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-accepted-bogoljubow-defense-uethn",
    "name": "Queen's Gambit Accepted: Bogoljubow Defense",
    "side": "Black",
    "tier": "free",
    "eco": "D24",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/1pp1pppp/p4n2/8/2pPP3/2N2N2/PP3PPP/R1BQKB1R b KQkq - 0 5",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Accepted.",
    "whyLearn": "Queen's Gambit Accepted: Bogoljubow Defense is identified by the canonical ECO D24 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Bogoljubow Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "a6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Bogoljubow Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-accepted-bogoljubow-defense-uethn-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Bogoljubow%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Bogoljubow Defense video lesson"
    }
  },
  {
    "id": "black-italian-game-deutz-gambit-5f66x",
    "name": "Italian Game: Deutz Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "C50",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/2b1p3/2BPP3/5N2/PPP2PPP/RNBQ1RK1 b kq - 0 5",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Italian Game.",
    "whyLearn": "Italian Game: Deutz Gambit is identified by the canonical ECO C50 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Deutz Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Deutz Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-italian-game-deutz-gambit-5f66x-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Deutz%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Italian Game: Deutz Gambit video lesson"
    }
  },
  {
    "id": "black-queen-s-gambit-accepted-winawer-defense-8t1kj",
    "name": "Queen's Gambit Accepted: Winawer Defense",
    "side": "Black",
    "tier": "free",
    "eco": "D25",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rn1qkb1r/ppp1pppp/4bn2/8/2pP4/4PN2/PP3PPP/RNBQKB1R w KQkq - 1 5",
    "idea": "Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Queen's Gambit Accepted.",
    "whyLearn": "Queen's Gambit Accepted: Winawer Defense is identified by the canonical ECO D25 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Queen's Gambit Accepted: Winawer Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "dxc4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc4 from d5 to c4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "e3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e3 from e2 to e3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be6 from c8 to e6. The move activates a bishop on a diagonal that influences the center or the enemy king. In Queen's Gambit Accepted: Winawer Defense, relate it to this course objective: Meet d4 with d5, challenge White's center, and develop into the recognizable Queen's Gambit Accepted structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-queen-s-gambit-accepted-winawer-defense-8t1kj-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Queen's%20Gambit%20Accepted%3A%20Winawer%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Queen's Gambit Accepted: Winawer Defense video lesson"
    }
  },
  {
    "id": "black-english-opening-king-s-english-variation-rever-1pnr0",
    "name": "English Opening: King's English Variation, Reversed Closed Sicilian",
    "side": "Black",
    "tier": "free",
    "eco": "A25",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "c4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk2r/pppp1ppp/2n2n2/3Np3/1bP5/6P1/PP1PPPBP/R1BQK1NR b KQkq - 6 5",
    "idea": "Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the English Opening.",
    "whyLearn": "English Opening: King's English Variation, Reversed Closed Sicilian is identified by the canonical ECO A25 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name English Opening: King's English Variation, Reversed Closed Sicilian as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nd5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nd5 from c3 to d5. The move develops a knight toward central outposts and adds support to the next pawn break. In English Opening: King's English Variation, Reversed Closed Sicilian, relate it to this course objective: Meet c4 with e5, challenge White's center, and develop into the recognizable English Opening structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-english-opening-king-s-english-variation-rever-1pnr0-branch-1",
        "opponentMove": "1.d4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to d4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=English%20Opening%3A%20King's%20English%20Variation%2C%20Reversed%20Closed%20Sicilian%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable English Opening: King's English Variation, Reversed Closed Sicilian video lesson"
    }
  },
  {
    "id": "black-italian-game-scotch-gambit-z996j",
    "name": "Italian Game: Scotch Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "C56",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pppp1ppp/2n2n2/8/2BpP3/5N2/PPP2PPP/RNBQ1RK1 b kq - 1 5",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Italian Game.",
    "whyLearn": "Italian Game: Scotch Gambit is identified by the canonical ECO C56 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Scotch Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "exd4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays exd4 from e5 to d4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Italian Game: Scotch Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-italian-game-scotch-gambit-z996j-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Scotch%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Italian Game: Scotch Gambit video lesson"
    }
  },
  {
    "id": "black-italian-game-two-knights-defense-15nqk",
    "name": "Italian Game: Two Knights Defense",
    "side": "Black",
    "tier": "free",
    "eco": "C55",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/ppp2ppp/2n5/3pp3/2B1N3/5N2/PPPP1PPP/R1BQK2R w KQkq - 0 6",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Italian Game.",
    "whyLearn": "Italian Game: Two Knights Defense is identified by the canonical ECO C55 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Two Knights Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nxe4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Two Knights Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-italian-game-two-knights-defense-15nqk-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Two%20Knights%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Italian Game: Two Knights Defense video lesson"
    }
  },
  {
    "id": "black-italian-game-evans-gambit-main-line-euezb",
    "name": "Italian Game: Evans Gambit, Main Line",
    "side": "Black",
    "tier": "free",
    "eco": "C52",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk1nr/pppp1ppp/2n5/b3p3/2B1P3/2P2N2/P2P1PPP/RNBQK2R w KQkq - 1 6",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Italian Game.",
    "whyLearn": "Italian Game: Evans Gambit, Main Line is identified by the canonical ECO C52 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Evans Gambit, Main Line as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "b4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays b4 from b2 to b4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bxb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bxb4 from c5 to b4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "c3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c3 from c2 to c3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Ba5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ba5 from b4 to a5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Evans Gambit, Main Line, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-italian-game-evans-gambit-main-line-euezb-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Evans%20Gambit%2C%20Main%20Line%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Italian Game: Evans Gambit, Main Line video lesson"
    }
  },
  {
    "id": "black-italian-game-evans-gambit-tlgid",
    "name": "Italian Game: Evans Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "C52",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "r1bqk1nr/ppp2ppp/2np4/b3p3/2B1P3/2P2N2/P2P1PPP/RNBQ1RK1 w kq - 0 7",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Italian Game.",
    "whyLearn": "Italian Game: Evans Gambit is identified by the canonical ECO C52 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Italian Game: Evans Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bc5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "b4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays b4 from b2 to b4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bxb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bxb4 from c5 to b4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "c3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c3 from c2 to c3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Ba5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ba5 from b4 to a5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 11,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Italian Game: Evans Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Italian Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-italian-game-evans-gambit-tlgid-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Italian%20Game%3A%20Evans%20Gambit%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Italian Game: Evans Gambit video lesson"
    }
  },
  {
    "id": "black-ruy-lopez-morphy-defense-1mbjz",
    "name": "Ruy Lopez: Morphy Defense",
    "side": "Black",
    "tier": "free",
    "eco": "C78",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/1ppp1ppp/p1n2n2/4p3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 b kq - 3 5",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Ruy Lopez.",
    "whyLearn": "Ruy Lopez: Morphy Defense is identified by the canonical ECO C78 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Morphy Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Morphy Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-ruy-lopez-morphy-defense-1mbjz-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Morphy%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Ruy Lopez: Morphy Defense video lesson"
    }
  },
  {
    "id": "black-ruy-lopez-central-countergambit-ozoqv",
    "name": "Ruy Lopez: Central Countergambit",
    "side": "Black",
    "tier": "free",
    "eco": "C78",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/1pp2ppp/p1n2n2/3pp3/B3P3/5N2/PPPP1PPP/RNBQ1RK1 w kq - 0 6",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Ruy Lopez.",
    "whyLearn": "Ruy Lopez: Central Countergambit is identified by the canonical ECO C78 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Central Countergambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Central Countergambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-ruy-lopez-central-countergambit-ozoqv-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Central%20Countergambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Ruy Lopez: Central Countergambit video lesson"
    }
  },
  {
    "id": "black-four-knights-game-italian-variation-noa-gambit-nyfgz",
    "name": "Four Knights Game: Italian Variation, Noa Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "C47",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pppp1Bpp/2n5/4p3/4n3/2N2N2/PPPP1PPP/R1BQK2R b KQkq - 0 5",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Four Knights Game.",
    "whyLearn": "Four Knights Game: Italian Variation, Noa Gambit is identified by the canonical ECO C47 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Four Knights Game: Italian Variation, Noa Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bc4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bc4 from f1 to c4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bxf7+",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bxf7+ from c4 to f7. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Four Knights Game: Italian Variation, Noa Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Four Knights Game structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-four-knights-game-italian-variation-noa-gambit-nyfgz-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Four%20Knights%20Game%3A%20Italian%20Variation%2C%20Noa%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Four Knights Game: Italian Variation, Noa Gambit video lesson"
    }
  },
  {
    "id": "black-ruy-lopez-alapin-defense-alapin-gambit-1iqi9",
    "name": "Ruy Lopez: Alapin Defense, Alapin Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "C60",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk1nr/ppp2ppp/2p5/b3p3/4P3/2P2N2/PP1P1PPP/RNBQK2R w KQkq - 0 6",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Ruy Lopez.",
    "whyLearn": "Ruy Lopez: Alapin Defense, Alapin Gambit is identified by the canonical ECO C60 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Alapin Defense, Alapin Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bb4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bb4 from f8 to b4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "c3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c3 from c2 to c3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Ba5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ba5 from b4 to a5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bxc6",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bxc6 from b5 to c6. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "dxc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxc6 from d7 to c6. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Ruy Lopez: Alapin Defense, Alapin Gambit, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-ruy-lopez-alapin-defense-alapin-gambit-1iqi9-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Alapin%20Defense%2C%20Alapin%20Gambit%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable Ruy Lopez: Alapin Defense, Alapin Gambit video lesson"
    }
  },
  {
    "id": "black-ruy-lopez-morphy-defense-graz-variation-1v6dv",
    "name": "Ruy Lopez: Morphy Defense, Graz Variation",
    "side": "Black",
    "tier": "free",
    "eco": "C70",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqk1nr/2pp1ppp/p1n5/1pb1p3/4P3/1B3N2/PPPP1PPP/RNBQK2R w KQkq - 2 6",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Ruy Lopez.",
    "whyLearn": "Ruy Lopez: Morphy Defense, Graz Variation is identified by the canonical ECO C70 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Morphy Defense, Graz Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Ba4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Ba4 from b5 to a4. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "b5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays b5 from b7 to b5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bb3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb3 from a4 to b3. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Bc5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bc5 from f8 to c5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Morphy Defense, Graz Variation, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-ruy-lopez-morphy-defense-graz-variation-1v6dv-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Morphy%20Defense%2C%20Graz%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Ruy Lopez: Morphy Defense, Graz Variation video lesson"
    }
  },
  {
    "id": "black-ruy-lopez-berlin-defense-15c6o",
    "name": "Ruy Lopez: Berlin Defense",
    "side": "Black",
    "tier": "free",
    "eco": "C65",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "r1bqkb1r/pppp1ppp/2n2n2/1B2p3/4P3/5N2/PPPP1PPP/RNBQ1RK1 b kq - 5 4",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Ruy Lopez.",
    "whyLearn": "Ruy Lopez: Berlin Defense is identified by the canonical ECO C65 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Ruy Lopez: Berlin Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bb5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bb5 from f1 to b5. The move activates a bishop on a diagonal that influences the center or the enemy king. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In Ruy Lopez: Berlin Defense, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Ruy Lopez structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-ruy-lopez-berlin-defense-15c6o-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Ruy%20Lopez%3A%20Berlin%20Defense%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Ruy Lopez: Berlin Defense video lesson"
    }
  },
  {
    "id": "black-french-defense-steinitz-variation-gajku",
    "name": "French Defense: Steinitz Variation",
    "side": "Black",
    "tier": "free",
    "eco": "C11",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/1ppn1ppp/p3p3/3pP3/3P4/2N2N2/PPP2PPP/R1BQKB1R w KQkq - 1 6",
    "idea": "Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the French Defense.",
    "whyLearn": "French Defense: Steinitz Variation is identified by the canonical ECO C11 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Steinitz Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "a6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays a6 from a7 to a6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e5 from e4 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Nfd7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nfd7 from f6 to d7. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Steinitz Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-french-defense-steinitz-variation-gajku-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Steinitz%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable French Defense: Steinitz Variation video lesson"
    }
  },
  {
    "id": "black-french-defense-classical-variation-ct8vk",
    "name": "French Defense: Classical Variation",
    "side": "Black",
    "tier": "free",
    "eco": "C13",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1bppp/4pn2/6B1/3PN3/8/PPP2PPP/R2QKBNR w KQkq - 1 6",
    "idea": "Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the French Defense.",
    "whyLearn": "French Defense: Classical Variation is identified by the canonical ECO C13 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Classical Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "dxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nxe4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Be7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Classical Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-french-defense-classical-variation-ct8vk-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Classical%20Variation%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Defense: Classical Variation video lesson"
    }
  },
  {
    "id": "black-petrov-s-defense-french-attack-w0iwy",
    "name": "Petrov's Defense: French Attack",
    "side": "Black",
    "tier": "free",
    "eco": "C42",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/ppp2ppp/3p4/8/4n3/3P1N2/PPP2PPP/RNBQKB1R b KQkq - 0 5",
    "idea": "Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Petrov's Defense.",
    "whyLearn": "Petrov's Defense: French Attack is identified by the canonical ECO C42 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Petrov's Defense: French Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nxe5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe5 from f3 to e5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from e5 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nxe4 from f6 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Petrov's Defense: French Attack, relate it to this course objective: Meet e4 with e5, challenge White's center, and develop into the recognizable Petrov's Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-petrov-s-defense-french-attack-w0iwy-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=Petrov's%20Defense%3A%20French%20Attack%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable Petrov's Defense: French Attack video lesson"
    }
  },
  {
    "id": "black-french-defense-hoffmann-gambit-fpyun",
    "name": "French Defense: Hoffmann Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "C00",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkbnr/ppp2ppp/8/3p4/3PPp2/8/PPP1Q1PP/RNB1KBNR w KQkq - 0 5",
    "idea": "Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the French Defense.",
    "whyLearn": "French Defense: Hoffmann Gambit is identified by the canonical ECO C00 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Hoffmann Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Qe2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Qe2 from d1 to e2. The move uses the queen for a specific task, so you must verify that enemy development cannot gain time by attacking it. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e6 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "f4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays f4 from f2 to f4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "exf4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays exf4 from e5 to f4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In French Defense: Hoffmann Gambit, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-french-defense-hoffmann-gambit-fpyun-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Hanging Pawns",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Hoffmann%20Gambit%20chess%20opening%20lesson%20Hanging%20Pawns",
      "label": "Find a reputable French Defense: Hoffmann Gambit video lesson"
    }
  },
  {
    "id": "black-french-defense-advance-variation-1i8ta",
    "name": "French Defense: Advance Variation",
    "side": "Black",
    "tier": "free",
    "eco": "C02",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "r1bqkbnr/pp3ppp/2n1p3/2ppP3/3P4/2P5/PP3PPP/RNBQKBNR w KQkq - 1 5",
    "idea": "Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the French Defense.",
    "whyLearn": "French Defense: Advance Variation is identified by the canonical ECO C02 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Advance Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "e5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e5 from e4 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "c3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c3 from c2 to c3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Advance Variation, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-french-defense-advance-variation-1i8ta-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Advance%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable French Defense: Advance Variation video lesson"
    }
  },
  {
    "id": "black-french-defense-alekhine-chatard-attack-590ge",
    "name": "French Defense: Alekhine-Chatard Attack",
    "side": "Black",
    "tier": "free",
    "eco": "C13",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/pppnbppp/4p3/3pP1B1/3P3P/2N5/PPP2PP1/R2QKBNR b KQkq - 0 6",
    "idea": "Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the French Defense.",
    "whyLearn": "French Defense: Alekhine-Chatard Attack is identified by the canonical ECO C13 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name French Defense: Alekhine-Chatard Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Bg5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg5 from c1 to g5. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Be7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Be7 from f8 to e7. The move activates a bishop on a diagonal that influences the center or the enemy king. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e5 from e4 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Nfd7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nfd7 from f6 to d7. The move develops a knight toward central outposts and adds support to the next pawn break. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "h4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays h4 from h2 to h4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In French Defense: Alekhine-Chatard Attack, relate it to this course objective: Meet e4 with e6, challenge White's center, and develop into the recognizable French Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-french-defense-alekhine-chatard-attack-590ge-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Daniel Naroditsky",
      "url": "https://www.youtube.com/results?search_query=French%20Defense%3A%20Alekhine-Chatard%20Attack%20chess%20opening%20lesson%20Daniel%20Naroditsky",
      "label": "Find a reputable French Defense: Alekhine-Chatard Attack video lesson"
    }
  },
  {
    "id": "black-caro-kann-defense-panov-attack-9qk8d",
    "name": "Caro-Kann Defense: Panov Attack",
    "side": "Black",
    "tier": "free",
    "eco": "B14",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/4pn2/3p4/2PP4/2N5/PP3PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay.",
    "structure": "An early exchange creates open or half-open files, so development speed and control of the remaining central pawns become the first priorities.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Caro-Kann Defense.",
    "whyLearn": "Caro-Kann Defense: Panov Attack is identified by the canonical ECO B14 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Panov Attack as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "exd5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays exd5 from e4 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "cxd5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays cxd5 from c6 to d5. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "e6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e6 from e7 to e6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Panov Attack, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-caro-kann-defense-panov-attack-9qk8d-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Panov%20Attack%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Panov Attack video lesson"
    }
  },
  {
    "id": "black-caro-kann-defense-alien-gambit-1owhu",
    "name": "Caro-Kann Defense: Alien Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp2pNp1/2p2n1p/8/3P4/8/PPP2PPP/R1BQKBNR b KQkq - 0 6",
    "idea": "Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Caro-Kann Defense.",
    "whyLearn": "Caro-Kann Defense: Alien Gambit is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Alien Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Ng5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Ng5 from e4 to g5. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "h6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays h6 from h7 to h6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 10,
        "san": "Nxf7",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxf7 from g5 to f7. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alien Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-caro-kann-defense-alien-gambit-1owhu-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Alien%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Alien Gambit video lesson"
    }
  },
  {
    "id": "black-caro-kann-defense-tartakower-variation-1schr",
    "name": "Caro-Kann Defense: Tartakower Variation",
    "side": "Black",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Moderate",
    "simplicity": 3,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3ppp/2p2p2/8/3P4/8/PPP2PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Caro-Kann Defense.",
    "whyLearn": "Caro-Kann Defense: Tartakower Variation is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Tartakower Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Nxf6+",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxf6+ from e4 to f6. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "exf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays exf6 from e7 to f6. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Tartakower Variation, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-caro-kann-defense-tartakower-variation-1schr-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Tartakower%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Tartakower Variation video lesson"
    }
  },
  {
    "id": "black-caro-kann-defense-alekhine-gambit-xb96g",
    "name": "Caro-Kann Defense: Alekhine Gambit",
    "side": "Black",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp2pppp/2p2n2/8/3PN3/3B4/PPP2PPP/R1BQK1NR b KQkq - 2 5",
    "idea": "Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Caro-Kann Defense.",
    "whyLearn": "Caro-Kann Defense: Alekhine Gambit is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense: Alekhine Gambit as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nxe4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nxe4 from c3 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "Bd3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bd3 from f1 to d3. The move activates a bishop on a diagonal that influences the center or the enemy king. In Caro-Kann Defense: Alekhine Gambit, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-caro-kann-defense-alekhine-gambit-xb96g-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%3A%20Alekhine%20Gambit%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Caro-Kann Defense: Alekhine Gambit video lesson"
    }
  },
  {
    "id": "black-caro-kann-defense-qiur5",
    "name": "Caro-Kann Defense",
    "side": "Black",
    "tier": "free",
    "eco": "B15",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "e4",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "rnbqkbnr/pp2pppp/2p5/8/3Pp3/2N5/PPP2PPP/R1BQKBNR w KQkq - 0 4",
    "idea": "Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay.",
    "structure": "The central pawns remain flexible. Avoid fixing the structure until you know which file, diagonal, or outpost your pieces need.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Caro-Kann Defense.",
    "whyLearn": "Caro-Kann Defense is identified by the canonical ECO B15 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Caro-Kann Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Caro-Kann Defense, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Caro-Kann Defense, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "dxe4",
        "color": "black",
        "role": "player",
        "explanation": "Black plays dxe4 from d5 to e4. The move resolves a concrete tension; the resulting files, diagonals, and pawn structure matter more than the exchange by itself. In Caro-Kann Defense, relate it to this course objective: Meet e4 with c6, challenge White's center, and develop into the recognizable Caro-Kann Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-caro-kann-defense-qiur5-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=Caro-Kann%20Defense%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable Caro-Kann Defense video lesson"
    }
  },
  {
    "id": "black-king-s-indian-attack-french-variation-1ry7a",
    "name": "King's Indian Attack: French Variation",
    "side": "Black",
    "tier": "free",
    "eco": "A08",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 5,
    "benchmark": 50,
    "explorerFen": "r1bqkbnr/pp2pppp/2n5/2pp4/8/5NP1/PPPPPPBP/RNBQK2R w KQkq - 2 4",
    "idea": "Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the King's Indian Attack.",
    "whyLearn": "King's Indian Attack: French Variation is identified by the canonical ECO A08 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: French Variation as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: French Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: French Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: French Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: French Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: French Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Nc6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nc6 from b8 to c6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: French Variation, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-king-s-indian-attack-french-variation-1ry7a-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20French%20Variation%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack: French Variation video lesson"
    }
  },
  {
    "id": "black-king-s-indian-attack-with-bf5-19c8u",
    "name": "King's Indian Attack, with Bf5",
    "side": "Black",
    "tier": "free",
    "eco": "A07",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rn1qkb1r/pp2ppp1/2p2n1p/3p1b2/8/3P1NP1/PPP1PPBP/RNBQ1RK1 w kq - 0 6",
    "idea": "Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the King's Indian Attack.",
    "whyLearn": "King's Indian Attack, with Bf5 is identified by the canonical ECO A07 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack, with Bf5 as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "c6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c6 from c7 to c6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "Bf5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bf5 from c8 to f5. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "h6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays h6 from h7 to h6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack, with Bf5, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-king-s-indian-attack-with-bf5-19c8u-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%2C%20with%20Bf5%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack, with Bf5 video lesson"
    }
  },
  {
    "id": "black-king-s-indian-attack-wahls-defense-1l5za",
    "name": "King's Indian Attack: Wahls Defense",
    "side": "Black",
    "tier": "free",
    "eco": "A05",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbq1rk1/ppp1ppbp/5np1/3p4/8/3P1NP1/PPP1PPBP/RNBQ1RK1 w - - 0 6",
    "idea": "Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay.",
    "structure": "A fianchetto structure gives a bishop a long diagonal. Preserve that bishop when it guards the king or restrains a central break.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the King's Indian Attack.",
    "whyLearn": "King's Indian Attack: Wahls Defense is identified by the canonical ECO A05 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: Wahls Defense as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "O-O",
        "color": "black",
        "role": "player",
        "explanation": "Black plays O-O from e8 to g8. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Wahls Defense, relate it to this course objective: Meet Nf3 with Nf6, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-king-s-indian-attack-wahls-defense-1l5za-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "ChessNetwork",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20Wahls%20Defense%20chess%20opening%20lesson%20ChessNetwork",
      "label": "Find a reputable King's Indian Attack: Wahls Defense video lesson"
    }
  },
  {
    "id": "black-benoni-defense-king-s-indian-system-1j30w",
    "name": "Benoni Defense: King's Indian System",
    "side": "Black",
    "tier": "free",
    "eco": "A56",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "d4",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqkb1r/pp3p1p/3p1np1/2pPp3/2P1P3/2N5/PP3PPP/R1BQKBNR w KQkq - 0 6",
    "idea": "Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the Benoni Defense.",
    "whyLearn": "Benoni Defense: King's Indian System is identified by the canonical ECO A56 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name Benoni Defense: King's Indian System as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "d4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d4 from d2 to d4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "Nf6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Nf6 from g8 to f6. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "c4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays c4 from c2 to c4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "c5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays c5 from c7 to c5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "d5",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d5 from d4 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "Nc3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nc3 from b1 to c3. The move develops a knight toward central outposts and adds support to the next pawn break. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "d6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d6 from d7 to d6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "e4",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays e4 from e2 to e4. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In Benoni Defense: King's Indian System, relate it to this course objective: Meet d4 with Nf6, challenge White's center, and develop into the recognizable Benoni Defense structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-benoni-defense-king-s-indian-system-1j30w-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=Benoni%20Defense%3A%20King's%20Indian%20System%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable Benoni Defense: King's Indian System video lesson"
    }
  },
  {
    "id": "black-king-s-indian-attack-pachman-system-19ojo",
    "name": "King's Indian Attack: Pachman System",
    "side": "Black",
    "tier": "free",
    "eco": "A07",
    "source": {
      "name": "Lichess chess-openings",
      "license": "CC0",
      "url": "https://github.com/lichess-org/chess-openings"
    },
    "responseTo": "Nf3",
    "complexity": "Simple",
    "simplicity": 4,
    "benchmark": 50,
    "explorerFen": "rnbqk2r/ppp1npbp/6p1/3pp3/8/3P1NP1/PPP1PPBP/RNBQ1RK1 w kq - 1 6",
    "idea": "Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay.",
    "structure": "The center can become locked; use the direction of the pawn chains to decide which wing has space and which pawn break attacks the base.",
    "plan": "Challenge White's center before it becomes stable, finish development, castle, and use the freeing pawn break associated with the King's Indian Attack.",
    "whyLearn": "King's Indian Attack: Pachman System is identified by the canonical ECO A07 position. Learning it from move one teaches both the route into the position and the strategic questions that remain after the named opening has been reached.",
    "mistakes": [
      "Treating the name King's Indian Attack: Pachman System as proof that the same plan works after every opponent reply."
    ],
    "mainline": [
      {
        "ply": 0,
        "san": "Nf3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Nf3 from g1 to f3. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 1,
        "san": "d5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays d5 from d7 to d5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 2,
        "san": "g3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays g3 from g2 to g3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 3,
        "san": "g6",
        "color": "black",
        "role": "player",
        "explanation": "Black plays g6 from g7 to g6. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 4,
        "san": "Bg2",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays Bg2 from f1 to g2. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 5,
        "san": "Bg7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Bg7 from f8 to g7. The move activates a bishop on a diagonal that influences the center or the enemy king. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 6,
        "san": "O-O",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays O-O from e1 to g1. The move secures the king and connects the rooks before the center opens. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 7,
        "san": "e5",
        "color": "black",
        "role": "player",
        "explanation": "Black plays e5 from e7 to e5. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 8,
        "san": "d3",
        "color": "white",
        "role": "opponent",
        "explanation": "White plays d3 from d2 to d3. The move changes the permanent pawn structure, claims space, and determines which squares the pieces can use. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      },
      {
        "ply": 9,
        "san": "Ne7",
        "color": "black",
        "role": "player",
        "explanation": "Black plays Ne7 from g8 to e7. The move develops a knight toward central outposts and adds support to the next pawn break. In King's Indian Attack: Pachman System, relate it to this course objective: Meet Nf3 with d5, challenge White's center, and develop into the recognizable King's Indian Attack structure before starting counterplay. Before copying it against another reply, check for forcing captures, checks, central breaks, and king safety; those details decide whether the same plan still works."
      }
    ],
    "branches": [
      {
        "id": "black-king-s-indian-attack-pachman-system-19ojo-branch-1",
        "opponentMove": "1.c4",
        "answer": "c5",
        "explanation": "c5 is a legal, practical reply to c4: it addresses the changed position by improving activity or central control. Recalculate instead of forcing the original sequence, then return to development, king safety, and the course's thematic pawn break."
      }
    ],
    "video": {
      "source": "Saint Louis Chess Club",
      "url": "https://www.youtube.com/results?search_query=King's%20Indian%20Attack%3A%20Pachman%20System%20chess%20opening%20lesson%20Saint%20Louis%20Chess%20Club",
      "label": "Find a reputable King's Indian Attack: Pachman System video lesson"
    }
  }
]
