ChessmateGet the appFEN
Forsyth-Edwards NotationFEN is a one-line text description of a single chess position and its relevant game state.
Its six fields describe piece placement, side to move, castling rights, an en-passant target, the halfmove clock, and the fullmove number.
FEN contains six fields
The fields describe piece placement, the active colour, castling availability, an en passant target square, the halfmove clock, and the fullmove number. Spaces separate the fields.
| Field | Start value | What it records |
|---|---|---|
| Piece placement | rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR | Every occupied and empty square |
| Active colour | w | White is to move |
| Castling | KQkq | Both sides retain both castling rights |
| En passant | - | No en passant target square |
| Halfmove clock | 0 | Plies since the last pawn move or capture |
| Fullmove number | 1 | Move number, increased after Black moves |
Piece placement is read from rank 8 to rank 1
Slashes separate ranks. Letters identify pieces, uppercase letters are White, lowercase letters are Black, and digits count consecutive empty squares within a rank.
8- Eight consecutive empty squares.
3k4- Three empty squares, a black king, then four empty squares.
FEN stores the current state, not the full history
FEN preserves the state needed to continue a game, including castling and en passant information. It does not list earlier moves, player names, comments, or variations; PGN is used for those records.
Under the original FEN specification, an en passant target is recorded after every two-square pawn advance even when no opposing pawn can legally capture there. FEN also cannot establish a threefold repetition claim by itself because it does not contain the earlier positions.