A FEN (Forsyth-Edwards Notation) is a single line of text that fully describes a chess position — every piece's square, whose turn it is, castling rights, and en passant status. It's what chess software actually passes around internally; any position on Chess.com, Lichess, or a chess book diagram can be reduced to one. You can get a FEN from a Chess.com or Lichess game by copying a move's position, or build one by hand on the Board Editor.
Paste one here to find out the objectively best move in that exact position, with no game history or prior moves needed — useful for checking a tricky spot from your own game, verifying a puzzle's solution, or just seeing what Stockfish thinks of a random position. The evaluation is in pawns from White's perspective: positive favors White, negative favors Black, and mate distances are shown directly when a forced checkmate exists.