Chess, whole

exhibit 0003 · sandbox

your move

how long it thinks

The whole engine is in this file — move generation, alpha-beta search with a transposition table, quiescence, and an evaluation that knows about passed pawns and about walking a lone king into the corner. Nothing is fetched; there is no server behind the board. Your game survives a closed tab.

A chess program is mostly a claim that it knows the rules. You can make it prove that one:
It counts every legal line from five awkward positions — castling through check, en passant pins, promotions — and compares the totals against the published ones. Add ?verify to the URL to run it on load, or ?fen= to set a position up.