Play a chess engine that tells you what it sees.
Claude wrote the rules, the search and the commentary on this page from one request. Click a piece to move it.
Thinking time
The engine has no opening book and no table of stored answers.
It generates every legal move from the rules and searches the tree of replies with alpha-beta pruning. Positions at the end of each line are scored by material and by where the pieces stand. On a laptop that comes to a few million positions for every second of thinking.
The commentary is assembled from what the search found. It reports the line the engine expects, how the evaluation moved after your last move, and any forced checkmate. Your pawns promote to queens.
Written by Claude as a single file with no libraries. The move generator was checked against published perft counts for five test positions before this page went up.