This chess variant uses the same board and pieces as standard chess, with extended options for the starting position and castling rules adapted accordingly.
Starting position:
- pawns start in the same position as in standard chess
- White pieces are placed randomly on the first rank
- the King must be placed somewhere between the Rooks
- the Bishops must be on opposite color squares
- Black pieces are placed equal and opposite to the White pieces
Castling rules:
- castling is allowed under the following conditions
- the King and the castling Rook must not have moved before
- no square between the King's initial and final squares may be under attack by any opposing piece
- all the squares between the King's initial and final squares and all the squares between the Rook's initial and final squares must be vacant except for the King and the castling Rook
- after castling, the Rook and King's final positions are exactly the same as they would be in standard chess
Games notation:
- games are recorded using the PGN notation, with an extension to the FEN notation in order to support castling information
- two very similar FEN extensions have been proposed: X-FEN and Shredder-FEN