Most chess moves follow the simple patterns in how to play chess. Three moves don't, and they're the ones beginners most often ask about. Here are the exact rules.
Castling
Castling is the only move in which two pieces move at once: your king and one rook. It tucks the king away to safety and brings the rook toward the center.
How: the king moves two squares toward the rook, and the rook jumps over the king to the square right next to it.
- Kingside (short castling, written O-O): king to g1, rook to f1 (for Black, g8 and f8).
- Queenside (long castling, written O-O-O): king to c1, rook to d1 (for Black, c8 and d8).
You can castle only if all of these are true:
- Neither the king nor that rook has moved yet in the game.
- All squares between them are empty.
- Your king is not in check right now.
- The king doesn't pass through or land on a square attacked by the opponent.
The rook may be attacked, and on the queenside the rook may pass an attacked square; only the king's path matters. In Rookfold, tap the king and the castling square shows as a possible move.
En passant
En passant ("in passing") is a special pawn capture.
When a pawn moves two squares forward from its starting square and lands right beside an enemy pawn, that enemy pawn may capture it as if it had moved only one square: it moves diagonally to the square the pawn passed over, and the pawn is removed.
- It must be done on the very next move, or the chance is gone.
- Only pawns can capture en passant, and only pawns can be captured this way.
Example: a white pawn on e5. Black plays d7–d5, landing next to it. White may answer exd6, capturing the d5 pawn.
Promotion
When a pawn reaches the far end of the board (rank 8 for White, rank 1 for Black), it must be promoted: it becomes a queen, rook, bishop or knight of your choice, right away.
- Most players choose a queen, the strongest piece.
- Sometimes a knight is better, for example when it gives check or avoids a stalemate.
- You can have more than one queen.
In Rookfold, a small window asks which piece you want.
Written down
In the move list, castling is O-O or O-O-O, en passant looks like any pawn capture (exd6), and promotion adds the new piece: e8=Q. Check is + and checkmate #. Next, learn the basic ways to checkmate.
