Chess

Goal

Checkmate the opposing king: attack it so no legal move can escape the threat.

Select a piece and destination

You play Ivory in these positions. Select a piece, then a legal destination. Use the mouse, touch, or Tab and Enter; arrow keys move focus between squares. Normal matches alternate Ivory and Onyx turns.

Advance a pawn

Practice example: Move the pawn from b2 to b3. The pawn advanced one square into an empty space. Pawns move forward but capture diagonally.

A pawn’s first move

From its starting rank a pawn may advance two squares if both are empty. A pawn cannot move backward, jump a blocker, or capture straight ahead.

Capture diagonally with a pawn

Practice example: Use the pawn on b3 to capture the Onyx rook on c4. The pawn moved one square diagonally forward onto an opponent, removing it.

Rooks follow ranks and files

A rook moves any clear distance horizontally or vertically. It may capture the first opposing piece in its path, but cannot pass through that piece or one of its own pieces.

Bishops follow diagonals

A bishop moves any clear distance diagonally. It stays on one square color and cannot jump over a piece.

The queen combines both paths

A queen moves any clear distance along a rank, file or diagonal. Its long reach does not allow it to jump over pieces.

Knights can jump

A knight moves two squares in one direction and one perpendicular square: an L shape. It can jump over intervening pieces, but its destination must be empty or occupied by an opponent.

Keep your king safe

A king normally moves one square in any direction. It cannot move onto an attacked square. Kings cannot stand next to one another, and you never win by capturing a king.

Escape check

Practice example: The rook attacks your king along the e-file. Move the king from e1 to d1. The king left the attacked file. Every legal reply to check must leave your own king safe.

Three ways to answer check

Depending on the position, you can move the king, capture the attacker, or block its line. A pinned piece cannot move if that exposes your king. A knight’s attack cannot be blocked between squares.

Castle on the king side

Practice example: Move the king from e1 to g1 to castle. The king moved two squares and the rook moved to f1 in the same turn.

Castling has conditions

The king and chosen rook must not have moved. Their path must be clear. The king cannot castle while checked or cross or land on an attacked square. Queen-side castling puts the king on c1 and rook on d1; Onyx uses rank 8.

Capture en passant

Practice example: Onyx just advanced its pawn from d7 to d5. Capture it with your pawn on e5 by moving to d6. The special capture landed on d6 and removed the pawn from d5. It was available only immediately after that two-square pawn move.

Promote a pawn

Practice example: Advance b7 to b8, then choose Queen in the promotion control. The pawn reached its final rank and became a queen. Promotion is part of that move.

Other promotion choices

You may choose a rook, bishop or knight instead of a queen. You can promote even if your original queen is still on the board. You cannot choose a king or leave the pawn unchanged.

Deliver checkmate

Practice example: Move the queen from f7 to g7 to checkmate the king on h8. The queen checks h8, every escape is covered, and the Ivory king protects the queen. The opponent has no legal reply.

No move without check is a draw

If the player to move has no legal move and the king is not checked, the result is stalemate, a draw. Having more material does not override stalemate.

Repeated positions

This engine automatically draws on the third occurrence of the same position, side to move, castling rights and en-passant field. It does not require a player to claim the draw.

The fifty-move limit

After 100 half-moves without a pawn move or capture, the engine declares a draw automatically. A pawn move or capture resets that counter.

Automatic material draws

This version automatically draws with kings alone, or kings plus one bishop or one knight. It does not detect every other dead position. There is no points score or match clock; the result is a win, loss or draw.

Normal match options

Choose a computer opponent or two people sharing the board. Against the computer you can choose your side. Difficulty changes the opponent’s search. Undo and Hint assist normal play; they do not change legal moves.