Create a new chess game and return its game_id. The server is the authoritative source of board state — never track the board yourself. Optionally pass a FEN to start from a custom position.

Delete a game and free its session.

Return the authoritative state of a game: FEN, turn, revision, check/mate/draw flags, move history, last move, castling rights. Use this instead of remembering the board. Set include_ascii=true to also get a board diagram.

Play a move (SAN like 'e4' or UCI like 'e2e4') and return the resulting state. This is the ONLY tool that mutates the game. expected_revision is required: pass the revision from your most recent game_state/move_candidates read. If the game has advanced since then, the move is rejected with STALE_POSITION.

List all legal moves in the current position (SAN, UCI, piece, capture, promotion).

Export the current game as PGN.

Import a PGN into a new game. Returns a new game_id with the position after all PGN moves. Rejects malformed or illegal PGN.

Run Stockfish on the current position and return the top engine lines (multipv). Scores are from the side-to-move perspective: positive cp = side to move is better; mate N = side to move mates in N. wdl is [win, draw, loss] in permille for the side to move. Use analysis_level (fast/normal/deep) or explicit depth/multipv. Does NOT mutate the game.

Return the Maia3 human-like move probability distribution for the current position, conditioned on a target Elo. Higher probability = more human-typical at that rating. This is NOT move quality — a high-probability move can still be objectively bad.

Evaluate one or more moves with Stockfish without mutating the game. Pass a single move string or an array of moves to compare. Returns, for each move, the score after the move (from the mover's perspective), cpLoss vs the best move, and a classification (best/excellent/good/inaccuracy/mistake/blunder).

The primary move-selection tool. Combine Stockfish objective evaluation (moverCp, whiteCp, cpLoss, mate, WDL), Maia3 human probability, and Lichess real-game statistics into a unified candidate list. moverCp is from the mover's perspective: higher = better for the player choosing the move. Use this before choosing a move; the final choice is yours.

Convenience layer over move_candidates: rank candidates for a strategic intent. This tool RANKS candidates but does NOT choose a move — use the returned signals and conversation context to make the final decision. Do not map user skill mechanically to an intent. intents: best (strongest engine move), strong (engine-strong but human-plausible), natural (most human-typical), balanced (blend of strength and human-likeness), ease_off (human-plausible moves that modestly reduce advantage without changing the expected result), give_chance (human-plausible inaccuracies that meaningfully improve the opponent's chances).

Query the Lichess opening explorer for real human game statistics in the current position (requires LICHESS_TOKEN).