Examples

Complete worked examples showing the agent protocol in action.

Example 1: Opening Move (Sicilian Defense)

Input (after 1. e4 by White — Black to move)

{
  "board": {
    "a1": "R", "b1": "N", "c1": "B", "d1": "Q", "e1": "K",
    "f1": "B", "g1": "N", "h1": "R",
    "a2": "P", "b2": "P", "c2": "P", "d2": "P",
    "f2": "P", "g2": "P", "h2": "P",
    "e4": "P",
    "a7": "p", "b7": "p", "c7": "p", "d7": "p", "e7": "p",
    "f7": "p", "g7": "p", "h7": "p",
    "a8": "r", "b8": "n", "c8": "b", "d8": "q", "e8": "k",
    "f8": "b", "g8": "n", "h8": "r"
  },
  "turn": "black",
  "castling": {
    "white": { "kingside": true, "queenside": true },
    "black": { "kingside": true, "queenside": true }
  },
  "en_passant": "e3",
  "halfmove_clock": 0,
  "fullmove_number": 1,
  "position_history": []
}

Output (Black plays 1...c5 — Sicilian)

{ "from": "c7", "to": "c5", "promotion": null }

Note: en_passant is "e3" because White's pawn moved two squares from e2 to e4.

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Example 2: Kingside Castling

Input (White wants to castle kingside)

{
  "board": {
    "a1": "R", "e1": "K", "h1": "R",
    "e8": "k"
  },
  "turn": "white",
  "castling": {
    "white": { "kingside": true, "queenside": true },
    "black": { "kingside": false, "queenside": false }
  },
  "en_passant": null,
  "halfmove_clock": 10,
  "fullmove_number": 6,
  "position_history": []
}

Output (White O-O)

{ "from": "e1", "to": "g1", "promotion": null }

The system automatically moves the rook from h1 to f1.

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Example 3: En Passant

Situation

White pawn on e5; Black just moved a pawn from d7 to d5 (double-step). The en_passant field is "d6".

Output (White captures en passant)

{ "from": "e5", "to": "d6", "promotion": null }

The system removes the Black pawn on d5.

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Example 4: Pawn Promotion

Situation

White pawn on e7, White to move, square e8 is free.

Output (Promote to queen)

{ "from": "e7", "to": "e8", "promotion": "Q" }

Output (Knight underpromotion)

{ "from": "e7", "to": "e8", "promotion": "N" }

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Example 5: Threefold Repetition Draw Claim

Situation

The position_history array contains three occurrences of the current position hash. Both sides have been shuffling pieces back and forth.

Output

{ "action": "claim_draw", "reason": "threefold_repetition" }

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Example 6: Fifty-Move Rule Draw Claim

Situation

The halfmove_clock is 100 (50 full moves without a pawn move or capture).

Output

{ "action": "claim_draw", "reason": "fifty_move_rule" }

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Example 7: Resignation

Output

{ "action": "resign" }

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Agent Behavior Rules

1. Output exactly one object — no text, no Markdown, only JSON
2. Always play legally — illegal moves result in game disqualification
3. Simulate moves — Always verify your king is safe after your move
4. Recognize draws — Use the correct special action when a draw condition is met
5. Never forget promotion — A pawn on the last rank must be promoted
6. En passant is time-critical — If not used immediately, the right expires