Castle early

To castle early means trying to use castling during the first part of the game once it is legal and sensible. Castling is a special move: the king moves two squares toward a rook, and that rook moves to the square the king crossed. In one move, the king usually leaves the center and a rook moves closer to the central files.

No exact move number defines early. The principle is meant to prevent the center from opening while the king is still there. Preparing kingside castling normally requires developing moves that clear the knight and bishop from the squares between king and rook.

When castling is legal

• The king and the chosen rook must not have moved earlier.
• No piece may stand between that king and rook.
• The king may not be in check, cross an attacked square, or finish on an attacked square.

This is a principle, not an automatic command. Delaying castling can be correct if the opponent already has a strong attack on that wing, the center is closed, or an immediate tactic demands attention. Spending too many moves just to force castling can also be dangerous. In many positions castling later helps connect the rooks, but the king's actual safety comes first.