Chess

Taken by you: Taken by the computer:

Tap a piece to see its moves, then tap where it should go · Undo takes back your last move

Turn: You

Computer strength

Your side

Moves

No moves yet.

The prompt

Make chess in one HTML file, player against computer. Complete rules: legal-move generation with castling, en passant and promotion, check, checkmate, stalemate, the fifty-move rule, threefold repetition and insufficient material. Check the move generator with perft counts. Computer: alpha-beta search with piece-square tables and capture-only quiescence, run in a Web Worker so the page stays responsive.

Claude wrote this game from a short brief like this one. It was then played, tested on phones and tuned before it went up here.

How to play

Each piece moves its own way. Tap a piece and dots show where it can go.
Put the enemy king in check with no escape (checkmate) to win.
Castling, en passant and promotion all work. When a pawn reaches the end you choose its new piece.
Your game is saved if you leave the page.

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Chess.