# Position At least one `position` command must be sent before each [[go]] command to inform the engine of the current game state. The first parameter indicates the initial game state from which moves in the second parameter have been played; either the standard chess starting position with `startpos` or a custom initial position with `fen` followed by a FEN string[^1]. > [!info] > The original standard is not completely clear on whether the GUI should leave the first parameter of `position` unchanged over the course of a game and just grow the list of moves in the second parameter, or if it is acceptable for the GUI to use an updated FEN string, and if so, when. > > I would suggest that engines should be capable of handling any interpretation, but that GUIs should (not must) update the FEN string occasionally to avoid the command getting too long, but not too frequently, to allow engines to avoid reconstructing their entire internal board representation on every move. --- ## Parameters - `startpos | fen <fenstring>` - Either just the [[Commands#Tokens|token]] `startpos`, or the token `fen` followed by a standard FEN string. Indicates the initial game state from which the moves in the second parameter have been played. - `moves <move1> ... <movei>` - The token `moves`, followed by a series of moves in [[Move Notation|UCI's own move notation variant]]. --- ## Examples - `position startpos` - Indicates that the current position is the standard chess starting position - `position startpos moves e2e4 e7e5` - One [[Fullmoves, Halfmoves, & Plies|fullmove]] after the start of the game, potentially the beginning of the King's Gambit - `position fen rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w AHah -` - Indicates the same position as the first example, just using FEN instead of the special case `startpos` [^1]: Forsyth-Edwards Notation (FEN) is a common notation used to completely describe a chess game state, including piece positions, player to move, castling rights, en passant target square, the halfmove clock, and the fullmove number. [Wikipedia](https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation)