Chess960

The pawns begin on their usual squares. White's other pieces are arranged on the first rank under three conditions: the king must stand between the two rooks, the bishops must occupy opposite-colored squares, and Black's pieces must be placed opposite their White counterparts. These restrictions create 960 starting positions, including the standard chess setup.

After setup, pieces move and capture as in ordinary chess, and the objective remains checkmate, meaning the opposing king is attacked with no legal reply.

The unfamiliar starting position reduces the value of memorizing exact opening sequences, but it does not remove ideas such as developing pieces, meaning moving them from their starting squares into useful play, coordinating them, and protecting the king. Each setup must be assessed immediately because a piece may begin active, blocked, or exposed in an unusual way.

Where castling finishes

The main rules difference is castling. After O-O, called g-side castling, the king finishes on g1 or g8 and the rook on f1 or f8. After O-O-O, called c-side castling, the king finishes on c1 or c8 and the rook on d1 or d8. Those final squares stay fixed even when the king and rook started elsewhere; in some setups only one of the two pieces actually has to move.

To castle, the chosen king and rook must not have moved. The squares needed by their paths must be clear except for those two pieces, and the king may not be in check, cross an attacked square, or finish on one. A platform's click or drag method may vary, but the rules require the same final position.