Premove

In online chess, a premove is a move input made by a player during their opponent's turn, taking effect only after the opponent moves. A premove is performed in the same way as a normal move, most commonly by dragging the piece to its destination, or by clicking the piece and then clicking its destination.

Premoving is available on chess websites such as the Internet Chess Club, the Free Internet Chess Server, Chess.com, and Lichess.

The Internet Chess Club allows players to block any players with premoving enabled.

Description
To premove, a player makes a move input in the same way as they would if it were their turn. After their opponent moves, the premove is immediately executed, provided that the resulting move is legal; otherwise, the premove is discarded. One can cancel a premove by clicking anywhere on the board; if only one premove is allowed at a time, then one can also cancel a premove by making another premove.

In general, a piece's premove options are dependent only on its location and type; no other considerations of the board state are relevant. For example, one can make a premove that would leave their king in check if it were their turn; one can premove a pawn capture even if there is no opposing piece to be captured; and so on. For a castling premove, it is also required that the rook to be castled with is present; additionally, it is generally required that the castling rights of the king and rook have been maintained. Such apparently impossible premoves are allowed because the opponent's upcoming move may change the position in a way that allows the premove to be executed.

Some websites, such as Chess.com, offer the option of making multiple premoves at a time. Each premove is executed in sequence if possible; however, if any premove fails to be executed, then it and all subsequent premoves in the sequence are cancelled.

Lichess offers the options to input moves with the keyboard and with one's voice; premoving is supported in these modes.

Strategy
Premoving is used both recreationally and to avoid letting one's clock run out. Generally, it is only done when either the move would be good in any subsequent position where it is valid or the player is in time trouble. It is most often used when anticipating a capture by an opponent so as to recapture the capturing piece. Premoves can be risky if the opponent anticipates it and/or does something unexpected, as in the Rosen Trap, a colloquial name for exploiting time trouble and an opponent using pre-moves to generate a stalemate in situations where a loss is otherwise assured using a move that is suboptimal in terms of keeping the game going longer but when combined with an opponent premoving based on the expectation of an optimal move, causes the player to have no legal moves.