Crazyhouse

Crazyhouse (also known as drop chess, mad chess, reinforcement chess, turnabout chess and schizo-chess) is a chess variant in which captured enemy pieces can be reintroduced, or dropped, into the game as one's own. The drop rule resembles that of shogi;[1] the two games are often compared though no evidence suggests one developing from the other. Crazyhouse is similar to bughouse chess; however, a game of Crazyhouse involves only two players.

1.N@e7+ Kh8 2.Bxg7# (@ notation)

Rules

The rules of chess apply except for the addition of drops, as explained below.

  • A piece that is captured reverses color and goes to the capturing player's reserve, pocket or bank, where it is considered held or in hand. At any time, instead of making a move with a piece on the board, a player can drop one of their held pieces onto an empty square on the board.[2]
  • A pawn may not be dropped on the 1st or 8th ranks.[3]
  • A pawn that is dropped on its 2nd rank may use its two-square initial advance; a pawn that is dropped on any other rank cannot.
  • When a piece that is promoted from a pawn is captured, it enters the opponent's reserve as a pawn.[3]

Unlike in shogi, dropping a pawn on a file containing another pawn of the same color and dropping a pawn to deliver checkmate are both permissible.[3]

Notation

Crazyhouse's notation system is an extension of the standard algebraic notation. A drop is notated by inserting an at sign between the piece type and the destination square unless the dropped piece is a pawn, in which case only the at sign and the destination square are used. For example, N@d5 means "knight is dropped on d5."[2]

FEN

There is no standard FEN specification for Crazyhouse. Lichess uses an extended version of FEN, adding a 9th rank as a reserve. Here is an example of Lichess's FEN implementation:[4]

r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4/PNNNbpp b - - 89 45

In XBoard/Winboard's notation system, the reserve is given in square brackets following the board position:

r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4[PNNNbpp] b - - 89 45

In Chess.com's notation system, the reserve is located after the full-move number.

To keep track of which pieces are promoted, Lichess and XBoard/Winboard use "~" after the letter designation. Chess.com uses the coordinates of the pieces.[5]

r2q1r1k/2p1ppb1/p2p2pp/3P1p2/B6B/2N2NPp/1PP2P1K/3Q3q w - - 0 26 NNBRpr h1

Variations

Crazyhouse has several related variants:

  • Loop Chess: A promoted piece keeps its rank when captured.[6]
  • Chessgi (also known as Mad Mate or Neo Chess): A promoted piece keeps its rank when captured. A pawn may be dropped on its 1st rank.[7]

See also
  • Hostage chess, a variant where a player can drop back into play their own previously captured pieces

References
  1. "Decoder of Crazyhouse". Retrieved 18 December 2022.
  2. "crazyhouse". FICS Help. Free Internet Chess Server. 2008-02-28. Archived from the original on 2014-04-16. Retrieved 2014-04-17.
  3. "crazyhouse". ICC Help. Internet Chess Club. Archived from the original on 2012-05-02. Retrieved 2014-04-17.
  4. ""IM opperwezen vs LM JannLee in T6Q3tMva : Analysis board • lichess.org"". Lichess. Archived from the original on 2018-05-26. Retrieved 2018-05-26.
  5. ""Chess: liviu78ro vs JannLeeCrazyhouse - 3367504566 - Chess.com"". Chess.com. Archived from the original on 2019-01-17. Retrieved 2019-01-17.
  6. "Game rules (Loop Chess)". BrainKing. Retrieved 2014-04-17.
  7. "Chessgi". ChessVariants.org. 2001-03-20. Archived from the original on 2014-03-27. Retrieved 2014-04-17.
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