What is Chess960?

Chess960 Video Chess960 Video Tutorial

Chess960 (also called Fischer Random Chess, Fischerrandom, and Fischerandom) is a variation of the game of chess characterized by a semi-random starting board position and special rules for castling.

Who invented it? When and where?

Former world chess champion Robert James "Bobby" Fischer introduced Fischer Random Chess (later to be renamed Chess960) on June 19, 1996, in Buenos Aires, Argentina. It was based on an existing chess variant called Shuffle Chess.

Why did he invent it?

Bobby Fischer was, by general agreement, one of the most naturally talented chess players of all time. The creativity and vision that infused his chess play were the result of an innate understanding of the principles of chess, rather than rote memorization of chess openings and techniques. As chess became increasingly popular throughout his life, Fischer became frustrated that marginally talented players could succeed through a determined memorization and analysis of chess openings. This frustration was reinforced by Fischer's experience playing against Soviet players of the 1960s and 1970s. Fischer believed that the success gained by many of these players was not due to innate talent, but rather to the government-sponsored, military-inspired "Soviet chess machine" that trained young Soviet players by emphasizing the memorization and analysis of chess openings and patterns. Similarly, Fischer believed that the recent dominance of chess computers was the result of their superior ability to instantly access a fixed and unchanging opening book.

In response, Fischer made a simple suggestion: create a system to randomize the starting position of a chess game. Specifically, his solution resulted in 960 possible opening positions. As a result, a human or computer would have to memorize not just one opening book, but 960 opening books! Certainly impossible for a human and quite challenging for a chess computer. In effect this would "level the playing field," requiring chess players to develop original moves and strategy based on the principles of chess, rather than making moves based on well-documented opening theory.

How is Chess960 different from traditional Chess? How is it the same?

Traditional Chess Board Chess960 Board

What's different:

  • The starting board position is randomly generated, subject to certain rules (see below).
  • The rules for castling are modified to take into account the fact that the initial positions of the rook and king will be different depending on the starting board position.

What's the same:

  • The chess board is made up of 64 squares in 8 files (columns) and 8 ranks (rows), with squares alternating between light and dark colors.
  • There are 16 chess pieces per side—8 pawns, 2 each of rooks, knights and bishops, 1 queen, and 1 king.
  • The movement of the pieces is the same as traditional chess, with the exception of castling.
  • The object of the game is to checkmate the opponent's king, i.e. to place the opponent's king under attack (in check) so that there is no way to remove it from attack on the next move. Additionally, one of the players may resign the game, or the game may end in a draw.

How is the Chess960 starting board position determined?

The starting board position is generated randomly. There are 960 possible board positions. Starting with the white pieces, the 8 pawns are placed on the 8 squares of the second rank just like in traditional chess. The pieces on the first rank are placed randomly, based on these criteria:

  • The king must be placed on a square between the two rooks.
  • The bishops must be placed on opposite-colored squares.

Once the white pieces are set, the black pieces are set up to mirror the white pieces, e.g. if the white king is on d1, the black king will be on d8. The king can never be on the a or h files as there would be no way to put it between two rooks.

The exact mathematical procedure for determining the position of the pieces on the 1st and 8th ranks is beyond the scope of this document. For the purposes of playing Chess960 on Caissa's Web, the starting board position will be generated for you, or you can choose one based on a Starting Position Identifier.

The Starting Position Identifier, or SPID, is a number between 0 and 959 and represents every possible starting board position. Note that SPID 518 is coincidentally the same starting board position as traditional chess. A Chess960 game that starts with this board position would proceed as a traditional chess game.

Chess960 is integrated with every feature of the Caissa's Web online chess website:
  • Live Online Chess

    Caissa's Web allows you to play live, real-time Chess960 games against both human and computer opponents. Put yourself on the Live Game Waiting List and specify you want to play a Chess960 game. Once paired, the starting board position will be randomly determined by the Caissa system and the game will begin. You can also use the Live Game Challenge function to challenge a specific member to a game of Chess960. As part of your challenge you can specify a starting position by entering a SPID number. If you do not choose a starting position, one will be randomly assigned.

    Chess960 Live Challenge

  • Correspondence Chess

    Put yourself on the Correspondence Game Waiting List and specify that you want to play a Chess960 game. When paired for a game, the Chess960 starting position will be automatically assigned by the system and the game will begin. You can also use the Correspondence Game Challenge to challenge a specific member to a game of Chess960.

  • Chess Tournaments

    Caissa's Web currently offers both Chess and Chess960 Correspondence Game tournaments. Regularly scheduled Chess960 Live Game tournaments are currently being planned.

  • Online Chess Tools

    Our free, web-enabled chess tools completely support the Chess960 game option. Using the PGN Editor, you can set up a Chess960 board position, add moves and create a PGN file; or you can import an existing Chess960 PGN file and edit it. Using the Chess Game Viewer, you can import a Chess960 PGN file for viewing. Using the Chess Diagram Generator, you can import a Chess960 PGN file for output as an animated graphics file.

    Chess960 PGN Editor

How to castle in Chess960

The basic castling move is the same for Chess960 as it is for traditional Chess, i.e. each player is allowed to castle once per game, moving both the king and a rook in a single move. However, due to the random positions of the king and rook in Chess960 games, certain modifications to the standard castling rules are applied. A summary of Chess960 castling is below.

  • After castling in Chess960, the final position of both the rook and king is the same as in standard chess. As an example, for white, queenside castling will always result in the king on c1 and the rook on d1. For kingside castling, the king will end up on g1 and the rook on f1.

  • The king and rook must not have moved yet in the game. This is known as the "unmoved" rule and is the same as in traditional chess.

  • For the king, no square between the starting square and the final square (including the starting and final squares) can be under attack by an opposing piece. This is known as the "unattacked" rule and is the same as in traditional chess.

  • All the squares between the king's starting and final squares (including the final square), and all of the squares between the rook's starting and final squares (including the final square), must be vacant except for the king and castling rook. This is known as the "unimpeded" rule and is slightly modified from traditional chess which requires only that the squares between the king and castling rook be vacant.

How to make the move. In traditional chess castling is usually carried out simply by moving the king to its destination square. This works because the king will move exactly two squares when castling, so the intention is always clear. However in Chess960, positions can occur in which the king will move only one square when castling (see the diagram above for an example; in playing O-O-O White's king goes from b1 to c1). In these cases moving the king to its destination square is ambiguous and may be interpreted as a simple king move. To clearly indicate that castling is desired, drag the king and release it ON TOP OF the rook you wish to castle with, as if you were "capturing" the rook. Note that this is sometimes counter-intuitive as it may involve moving the king in the direction opposite its final square (see again the diagram above, in which White's O-O-O would be entered as Kb1-a1). To avoid confusion, Caissa's Web also provides "O-O" and "O-O-O" buttons adjacent to the board when playing a game. Just click the appropriate button and the corresponding castling move will be entered for you automatically.


In summary, here is a complete Chess960 game for your viewing pleasure.

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