FEN: a practical example
A complete FEN string includes piece placement, the side to move, castling rights, an en passant target, the halfmove clock, and the fullmove number. Two boards with identical pieces can have different legal possibilities because these additional fields differ.
How to use the idea in your games
When sharing a position with an engine or AI assistant, include the full FEN rather than only a screenshot. A missing side-to-move field can completely reverse the tactical question.
A useful study question
Can you explain fen in your own words, identify it in a position, and describe when the idea does not apply? Test the explanation on a legal board before relying on it.
Connect the ideas
PGN, Chess engine, Castling are useful next concepts. Follow the links to compare definitions and examples, then return to the complete chess glossary whenever an unfamiliar term appears.
Sources & further reading
References checked September 5, 2026. Linked services are independent of ChessRankings.com™.