The rules for chess960 are simple (hear Fischer’s short explanation):
There are only two things you need to know over and above classical chess: (a) how to generate a starting position, and (b) how to castle.
How to generate a position
The pieces are randomly placed on the back row, with the pawns on the next row, as usual. There must always be:
- One rook to the left of the king, and one rook to the right of the king.
- One bishop on a light coloured square, and one bishop on a dark coloured square.
The starting positions are always symmetrical (as in regular chess). DGT have released a chess960 clock (DGT960 Pocket Timer) that will generate start positions, although there is software to do this also. For casual play, it’s simple to set up a valid position by hand. For offline reference, here is a PDF of all possible chess960 starting positions with associated ID numbers (if you’re looking for the classical start position, it’s 518).
How to castle
Castling in chess960 is very easy: No matter the starting position, the king and rook always go to the same final squares as in regular chess. In other words, the castling destinations (either queenside or kingside) are identical to the castling destinations in standard chess. This means, irrespective of which of the 960 starting positions you are playing, O-O (for white) would find the king on g1 and the rook that was to the right of the king on f1. O-O-O would find the king on c1 and the rook that was to the left of the king on d1.
The following diagram shows O-O for white, and O-O-O for black (which remain the same for any chess960 starting position):
As in regular chess, you may not castle:
- on a particular wing if you have moved that wing’s rook already.
- if you have moved the king already.
- if any squares the king must travel over are attacked.
- if any squares that rook and king must travel on to reach their destination are occupied by other pieces.
- if the king is in check.
The castling rules (and the bishop rule) form an important link to the history of chess. It is true that you may not always want to castle, but if you need to vacate the centre, switch wings, connect your rooks, etc, the option is there. The variant chess480 was presented as an improvement over chess960, but sports modified castling rules that often make the manoeuvre undesirable (e.g. by castling the king onto the d or e files).