FEN (Forsyth-Edwards Notation) is a standardized text format that describes a complete chess position in a single line of text. It encodes the location of every piece on the board, which side is to move, castling rights, en passant possibilities, and move counters.
A FEN string consists of six space-separated fields. The first describes piece placement rank by rank, from rank 8 down to rank 1: uppercase letters represent White’s pieces (K=king, Q=queen, R=rook, B=bishop, N=knight, P=pawn), lowercase letters represent Black’s pieces, and digits indicate the number of consecutive empty squares. For example, the starting position is written: rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1. The remaining fields specify who is to move (w or b), available castling rights (KQkq, or - if none remain), any en passant target square, the half-move clock for the fifty-move rule, and the full move number.
In practice, FEN is an essential tool for any player who works with analysis software. It lets you load any position instantly into an engine, a website, or a mobile app — without replaying every move from the start. Knowing how to copy and paste a FEN string lets you share or import a specific position in seconds.