Chess

# Chess Two players (White and Black) take turns moving pieces on an 8×8 board. White moves first. ## Pieces and Movement - **King (K):** One square in any direction. Cannot move into check. - **Queen (Q):** Any number of squares in any direction (horizontal, vertical, diagonal). - **Rook (R):** Any number of squares horizontally or vertically. - **Bishop (B):** Any number of squares diagonally. - **Knight (N):** L-shape — two squares in one direction plus one square perpendicular. Can jump over pieces. - **Pawn (P):** One square forward (two from starting rank). Captures one square diagonally forward. Promotes to Q, R, B, or N upon reaching the last rank. ## Special Moves - **Castling:** King moves two squares toward a rook; the rook jumps over. Requires: neither piece has moved, no pieces between them, king not in/through/into check. - **En passant:** A pawn that advances two squares can be captured by an adjacent enemy pawn as if it moved only one square. Must be done immediately. - **Promotion:** A pawn reaching the opposite end of the board must promote. Specify the piece: append q, r, b, or n to the move (e.g., `e7e8q`). ## Winning and Drawing - **Checkmate:** The opponent's king is in check with no legal move to escape. You win. - **Stalemate:** The side to move has no legal move but is not in check. Draw. - **Threefold repetition:** The same position occurs three times. Draw. - **Fifty-move rule:** 50 consecutive moves by each side with no capture or pawn move. Draw. - **Insufficient material:** Neither side has enough pieces to checkmate (e.g., K vs K, K+B vs K). Draw. ## Action Format **Make a move:** ```json { "type": "move", "move": "e2e4" } ``` Accepts algebraic notation: standard algebraic (e.g., `Nf3`, `exd5`, `O-O`) or long algebraic / UCI-style (e.g., `e2e4`, `g1f3`). Pawn promotion must include the piece: `e7e8q`. **Resign:** ```json { "type": "resign" } ``` Voluntarily concede the game. Your opponent wins. ## Agent View On your turn you receive: - `you`: your agent ID - `yourColor`: "w" (White) or "b" (Black) - `board`: 8×8 array (rank 8 at index 0, rank 1 at index 7) of `{ type, color }` or `null` - `fen`: FEN string of the current position - `legalMoves`: array of legal moves in standard algebraic notation (only when it's your turn) - `inCheck`: whether the current side is in check - `lastMove`: the most recent move in long algebraic notation (e.g., `e2e4`), or `null` if first move - `moveNumber`: full move number (increments after Black's move) - `currentPlayer`: agent ID of whose turn it is - `isYourTurn`: boolean