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Your prompt template can access the board state, the move history, and a list of legal moves, and the game engine selects the first legal move in the string response from the LLM you query.
My best prompt so far ignores the board state and the move history and just tries to play mates, make captures, and promote pawns. Can you do better?
The best prompt I came up with was: ``` You will be given a list of legal chess moves, LEGAL_MOVES. Pick one of them. Rules, in order of decreasing priority: 1. CHECKMATE. If one or more moves contains #, select a move that contains a #. 2. CAPTURE. If one or more moves contains x, select a move that contains x. 3. PROMOTION. If one or more moves contains =, select the move that contains =. 3. PAWN MOVE. Select a move that does not contain capital letters. 4. RANDOM MOVE. Select any move from the list. Go through the list of rules in order, stating whether the rule applies. If a rule does apply, use it to select your move.
Example 1: LEGAL_MOVES: Nf7, Rh2, g3, g4, Qxg8, Qg4#, Qc6, Qd6, Rb3, Rb2, Rb1 RESPONSE: Rule CHECKMATE applies. Qg4# contains a #. SELECTED MOVE: Qg4#
Example 2: LEGAL_MOVES: Nf7, Rh2, g3, g4, Qxg8, Qc6, Qd6, Rb3, Rb2, Rb1 RESPONSE: Rule CHECKMATE: No. Rule CAPTURE applies. Qxg8 contains x. SELECTED MOVE: Qxg8
Example 3: LEGAL_MOVES: Nf7+, Rh2, g3, g4, Qc6, Qd6, Rb3, Rb2, Rb1 Rule CHECKMATE: No. Rule CAPTURE: No. Rule PROMOTION: No. Rule PAWN MOVE applies. g3 does not contain a capital letter. SELECTED MOVE: g3.
Example 4: LEGAL_MOVES: Ne7+, Na7, Nd6, Nb6, Bh8, Bg7, b8=Q, Bf6, Ba1, Kh3, Kh1, Kg1, Rf2, Re2, Rd2, Rc2, Rb2, Ra2, Rg1 Rule CHECKMATE: No. Rule CAPTURE: No. Rule PROMOTION applies. b8=Q contains =. SELECTED MOVE: b8.
Example 5: LEGAL MOVES: Nf7, Rh2, Qc6, Qd6, Rb3, Rb2, Rb1 Rule CHECKMATE does not apply. Rule CAPTURE does not apply. Rule PROMOTION does not apply Rule PAWN MOVE does not apply. Rule RANDOM MOVE applies. Selected move: Nf7.
Example 6: LEGAL_MOVES: Na3, Nd2, Nc3, b3, b4, c5, Rh5+, Rh3, Rh2, Rh1, Kc2, Kd2, Ke1, Ng1, Nd4, Ng3, h7, g5 Rule CHECKMATE: No. Rule CAPTURE: No. Rule PROMOTION: No. Rule PAWN MOVE applies. h7 does not contain a capital letter. SELECTED MOVE: h7.
Example 7: LEGAL MOVES: Na3, Nc3, Ra2, Ra3, Ra4, Bb2, Ba3, Bd2, Be3, Kd2, Ke2, Kf1, Kf2, exd5, fxe5, Rh2, Rh3 Rule CHECKMATE: No. Rule CAPTURE applies. exd5 contains x. SELECTED MOVE: exd5
LEGAL MOVES: !legal_moves! RESPONSE: ```
It uses chain-of-thought and examples with reasoning. It also largely ignores most known concepts of chess strategy and focuses only on priors about what good moves look like as strings. Definitely curious to see if anyone can get something that's capable of delivering checkmate while working more "chessically".