Laws of Chess - Chess960

Chess960 offers 960 possible starting positions. The starting position Chess960 must meet the following rules:

  • White pawns are placed on their orthodox home squares.
  • All remaining white pieces are placed on the first rank.
  • The white king is placed somewhere between the two white rooks.
  • The white bishops are placed on opposite-colored squares.
  • The black pieces are placed equal-and-opposite to the white pieces. For example, if white's king is placed on B1, then black's king is placed on B8.

There are many differnet procedures for creating a starting position. Within the computer takes over this task if requested.

Once the initial position is set up, the rules for play are the same as standard chess. Each player´s objective is to checkmate their opponent´s king.

Chess960 allows each player to castle once per game. However, castling may only occur under the following conditions, which are extensions of the standard rules for castling:

  • After castling, the rook and king´s final positions are exactly the same positions as they would be in standard chess. Thus, after A-side castling (notated as O-O-O and known as queen-side castling in standard chess), the King is on C (C1 for White and C8 for Black) and the Rook is on D (D1 for White and D8 for Black). After H-side castling (notated as O-O and known as king-side castling in orthodox chess), the King is on G and the Rook is on F.
  • All the squares between the king´s initial and final squares (including the final square), and all of the squares between the rook´s initial and final squares (including the final square), must be vacant except for the king and castling rook.
  • Castling cannot capture any pieces.
  • The king and castling rook cannot "jump" over any pieces other than each other.
  • A player may castle at most once in a game. If a player moves his king or both of his initial rooks without castling, he may not castle during the rest of the game. Also he may not castle with a rook who has allready been moved.
  • The king may not be in check before or after castling.
  • All of the squares between the king´s initial and final squares (including the initial and final squares) must not be under attack by any opposing piece.

How to castle: Move the king by drag & drop over the field of the rook you want to castle with.

Recording the game

Since the initial position is usually not the orthodox chess initial position, recorded games must also record the initial position. Games recorded using the Portable Game Notation (PGN) can record the initial position using Forsyth-Edwards Notation (FEN), as the value of the "FEN" tag. Castling is marked as O-O or O-O-O, just as in standard chess. Note that not all chess programs can handle castling correctly in Chess960 games (except if the initial position is the standard chess initial position). To correctly record a Chess960 game in PGN, an additional "Variant" tag must be used to identify the rules; the rule named "Fischerandom" is accepted by many chess programs as identifying Chess960.

FEN is capable of expressing all possible starting positions of Chess960. However, unmodified FEN cannot express all possible positions of a Chess960 game. In a game, a rook may move into the back row on the same side of the king as the other rook, or pawn(s) may be underpromoted into rook(s) and moved into the back row. If a rook is unmoved and can still castle, yet there is more than one rook on that side, FEN notation as traditionally interpreted is ambiguous. This is because FEN records that castling is possible on that side, but not which rook is still allowed to castle. A modification of FEN, FRC-FEN, has been devised to remove this ambiguity. In FRC-FEN, the castling markings "KQkq" have their expected meanings: "Q" and "q" means A-side castling is still legal (for white and black respectively), and "K" and "k" means H-side castling is still legal (for white and black respectively). However, if there is more than one rook on the baseline on the same side of the king, and the rook that can castle is not the outermost rook on that side, then the column letter of the rook that can castle is appended right after the related "K", "k", "Q", or "q". In other words, in FRC-FEN notation, castling potentials belong to the outermost rooks by default. This means that the maximum length of the castling value is 8 characters instead of 4 (KkQq plus 4 disambiguation characters), though positions needing that many characters are extremely improbable.


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