Standard chess against the computer. You choose the engine level (1-5) and your color (white, black or random). White moves first; if you play Black, the engine's first move is already on the board when the game starts. The engine replies immediately after each of your moves.
\nBoard and coordinates. Files are the letters a-h from White's left to right, and ranks are the numbers 1-8 from White's side to Black's side, so White's king starts on e1 and Black's on e8. The text board is always drawn from your side (your pieces at the bottom) with files and ranks labeled on every edge. Uppercase letters are White pieces and lowercase letters are Black pieces: K king, Q queen, R rook, B bishop, N knight, P pawn, and . is an empty square.
Moves. Send a move in standard algebraic notation (SAN): e4, Nf3, Bxe5, O-O (kingside castle), O-O-O (queenside), exd8=Q (capture and promote). Check marks (+, #) are optional. You can also send UCI coordinates: e2e4, e1g1 (castling), e7e8q (promotion; a missing piece letter means a queen). Illegal or unclear moves are rejected with the full list of legal moves, and nothing changes. moves lists your legal moves grouped by piece.
End of the game. Checkmate wins. Stalemate, insufficient material, threefold repetition and the 50-move rule are draws and are applied automatically (no claim needed). A game that reaches 500 moves each is also a draw. draw offers a draw: the engine accepts only if it thinks it's at least half a pawn worse, and a declined offer costs nothing. resign ends the game as a loss.
Levels. Every level uses Stockfish 18 Lite; lower levels search less deeply and choose among its candidate moves with some randomness. 1 Beginner: about a third of its moves are random, so it hangs pieces; a casual player can beat it. 2 Casual: sees simple captures and threats but still blunders. 3 Club: solid tactics, rarely blunders. 4 Expert: very hard for humans. 5 Master: a full Stockfish search of about half a million positions per move, far beyond human strength.
\nScore. Let L be the level and n the number of moves you made. A win scores L x (100 + max(0, 60 - n)), so faster wins score more. A draw scores 40 x L. A loss (including resigning) scores 5 x L + min(n, 30). Higher levels are worth much more.