Crazyhouse chess is a chess variant that is similar to bughouse chess, but can be played with just two players. The game follows most of the normal rules of chess, except that captured pieces can be reintroduced to the board on the players side as their own. The game was derived as a two-player, single-board variant of bughouse chess. The drop rule in Crazyhouse is reminiscent of shogi, but there is no known evidence suggesting that shogi provided direct inspiration for the gameplay of bughouse or crazyhouse.

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

• A captured piece reverses color and goes to the capturing players pocket.
• At any time, instead of making a move with a piece on the board, a player can drop a piece from their pocket onto an empty square on the board.
• Drops resulting in immediate checkmate are permitted.
• Pawns may not be dropped on the players 1st or 8th ranks.
• Pawns and knights increase in relative importance in Crazyhouse, while rooks, queens, and bishops decrease in relative importance.

Crazyhouse has several related variants, such as Loop Chess and Chessgi. In Loop Chess, a promoted piece keeps its rank when captured, while in Chessgi, a pawn may be dropped on its 1st rank.

Overall, Crazyhouse chess is a fun and challenging variant of chess that requires players to think creatively and strategically.