4.4 Castling, en passant & promotion

4.4.1 Castling (short and long)#

Standard castling

1. Move the king first, two squares toward the rook.
2. Follow the board’s indication and move the rook to its castling square.
3. The castling dialog closes when both pieces are placed correctly.

Chess960: king destination occupied by the rook

1. Lift the king.
2. Lift the rook.
3. Place the king on its castling destination.
4. Place the rook on its new square.

When your opponent castles

The board indicates the king move and then the rook move. You can place both pieces on their final squares together; moving the opponent’s rook first is allowed. The app’s dialog shows both destinations and can also be closed with Ignore.

4.4.2 En passant (capturing in passing)#

En passant is available immediately after an opposing pawn moves two squares and lands beside your pawn. The right to capture is lost if you do not use it on your next move.

1. Move your capturing pawn diagonally to the square behind the opponent’s pawn.
2. Remove the captured pawn when its square lights red.

4.4.3 Pawn promotion#

Promote your pawn

1. Remove the pawn from the penultimate rank.
2. Place your chosen promotion piece on the final square. For standard chess, choose a queen, rook, bishop or knight.
3. If the promotion is also a capture, remove the captured piece before placing the promoted piece.

Non-standard variants can allow other pieces, such as a king in Antichess.

If you leave the pawn on the final rank

The square flashes red three times and stays red until you replace the pawn with a valid promotion piece.

When your opponent promotes

The app shows the selected piece and the destination square. Replace the pawn as indicated. The dialog closes when the physical position is correct, or you can dismiss it with Ignore.