Castling: when you can and when you can't

Castling is the only move in chess in which two pieces move at once: the king moves two squares towards the rook, and the rook jumps to the square immediately behind it. It serves two purposes at once - it hides the king behind the pawns and brings the rook into play.

In short: castling is legal when neither the king nor the chosen rook has moved yet, the squares between them are empty, and the king is not in check, does not pass through a captured square and does not land on a captured square. The short one (O-O) goes towards tower h, the long one (O-O-O) goes towards tower a. Try all three scenarios on the board below.

Try it live

Five conditions for legal castling

1. The king wasn't moving yet — not once in the entire batch. Returning to the starting field does not restore anything (check the "Law Lost" preset).
2. The selected tower has not moved yet — the movement of one rook does not deprive the right to castle with the other.
3. The squares between the king and the rook are empty.
4. The king is not in check - castling cannot "run away" from the shah.
5. The king does not pass through or land on the battlefield — none of the squares on the king's route can be attacked. Note: This condition applies to the king, not the rook - the rook can pass through the battlefield.

Short or long?

Short castling (O-O) is faster to set up - you just need to develop two pieces - and usually safer because the king lands behind intact pieces. Long (O-O-O) requires the development of three pieces, but immediately places the rook on the central d column and often announces a sharp game with attacks on opposite wings. For beginners, a good rule of thumb is to castle short and early, usually in the first ten moves.

Frequent doubts

• Does the Shah take away the right to castling? No - if you defended with a screen or capture (without moving the king), the law stands. Only the movement of the KING or a given tower is lost.
• Can you castle while a tower is under attack? Yes - the "field" conditions apply only to the king's route.
• How to save it? Short: O-O, long: O-O-O - these are the only moves in the notation without a field name.

Why does not castling cost so much?

The king in the center is the most common reason for beginners to lose quickly: open lines in the center of the board lead straight to it, and the rooks do not cooperate. That's why "forgotten castling" is on the list of the most common mistakes in the guide how to play chess — and the computer in training mode will punish procrastination mercilessly.

Castling is one of three special rules - the others are beating in passing and promotion of the division. All of them together, with the full set of rules, can be found on the website rules of chess.

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