Chess
Full-rules chess against a search-based computer or another person on the same device, with castling, en passant, promotion and every draw condition.
Moves
Rules people get wrong
- Castling is illegal out of check, through an attacked square, or into one — but it is perfectly legal with the rook attacked, and legal after the rook has passed through an attacked square on the queenside.
- En passant is only available on the move immediately after the pawn goes two squares. Miss it and the right is gone for good.
- Stalemate is a draw, not a win. Trapping a lone king with no legal move and no check throws away the whole game, and it is the most common way a winning endgame gets thrown.
- A pawn reaching the far rank can become a rook, bishop or knight as well as a queen. Underpromotion to a knight is occasionally the only move that works, usually because it comes with check.
- King and bishop against king cannot be mated, and neither can king and knight. The game is drawn the moment the last pawn goes, whatever the clock says.
- Threefold repetition counts positions, not moves — the same position with the same side to play and the same castling and en passant rights, three times over.
Your record, level by level
This table is kept in this browser only — nothing here is uploaded, and clearing site data clears it. The two global boards below are separate: a result goes to them only if you choose to put your name on it. A draw counts half a point and holds a winning streak rather than ending it. Best win is measured in moves, and only games against the computer are recorded.
How to use
- Pick the computer or another person, a difficulty, and which colour you want.
- Click one of your pieces, then click a highlighted square.
- Promote a pawn by choosing the piece you want when the prompt appears.
Frequently asked questions
Are all the awkward rules implemented?
Yes — castling with its full legality conditions, en passant including the case where taking would expose your own king, promotion to any of the four pieces, and all five ways a game can be drawn. Move generation is verified against published perft node counts, which is how chess programs are actually checked for correctness.
Why can I not castle?
One of five reasons: the king or that rook has already moved, a piece is in the way, you are in check, the king would pass through an attacked square, or it would land on one. Note that castling is legal when the ROOK is attacked, and queenside castling is legal even when b1 or b8 is attacked, because the king never crosses that square.
Why did my en passant capture disappear?
The right lasts exactly one move. If you do not take immediately after the enemy pawn moves two squares, it is gone for good. It is also illegal if making the capture would leave your own king in check, which happens when both pawns sit on the same rank as your king and an enemy rook or queen.
Do I have to promote to a queen?
No, and occasionally you should not. Rook, bishop and knight are all offered. Underpromotion to a knight is sometimes the only move that works, usually because it arrives with check; promoting to a rook or bishop is almost always a way to avoid stalemating your opponent.
What counts as a draw?
Stalemate, threefold repetition of the same position, fifty moves by each side without a capture or pawn move, and insufficient material — king against king, king and bishop, king and knight, or bishop against bishop. All four are detected automatically.
How strong is the computer?
It searches between one and four moves ahead depending on the difficulty, scoring material and piece placement. Tough is genuinely awkward for a casual player but well short of a strong club player — it has no opening book and no endgame knowledge.
Why does the computer take a moment to move?
It is searching, and the search grows sharply with depth. The board repaints before the search starts so it is clear the game has not frozen.
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