UCI move notation

UCI stands for Universal Chess Interface, a text protocol through which a graphical interface communicates with a chess engine. Within that protocol, an ordinary move is sent as a compact string containing its origin square and destination square.

Each square uses a file letter from a to h and a rank number from 1 to 8. Thus e2e4 means move from e2 to e4. The string contains no moving-piece letter, capture sign, or check marker. The program derives those facts from the current position.

A promotion adds a fifth lowercase letter: q for queen, r for rook, b for bishop, or n for knight. Castling, the combined king-and-rook move, is encoded as a king move, such as e1g1 for White's kingside castling in standard chess.

The move string is only one part of the UCI protocol. Separate commands set the position, start a search, and return the best move. It also differs from Smith notation, which may append an indicator for the captured piece.