chess-explain

Explains why lichess's engine move is better. Stockfish runs in the browser.

Lichess shows you the engine's best move. chess-explain tells you why that move, and not the one you played. Open a game on lichess's analysis board, step to a position and click Explain. The side panel compares lichess's top move with the move played in the game (or any move you type), and explains the difference in plain language: the tactic that refutes the played move, the threat it ignored, or the positional reason one move is better. How it works: - Stockfish 19 runs in your browser and analyses both moves: the evaluation after every move of each line, captures, checks, attacks, trapped pieces and the opponent's threats. - Stockfish 15's classical evaluation terms (mobility, king safety, pawn structure, ...) explain the positional part. - Claude turns those engine facts into a short explanation, without inventing moves. You need your own Anthropic API key. It stays in your browser and is sent only to Anthropic. Fair play: chess-explain only works where lichess itself shows its engine, and before every explanation it asks lichess whether you are playing a game. If you are, it refuses.