How the match works
Moves first, position when needed
A move sequence or PGN is matched to the longest named line in the opening reference. The finder also compares the resulting board position, side to move and castling rights. That second check catches a known transposition instead of stopping at a broader opening family.
The names, moves and ECO codes come from the CC0-licensed Lichess chess-openings project. A name identifies an opening, not whether a move is best. Use the analysis board when you want a Stockfish evaluation.
FAQ
Opening names and transpositions
How do I find the name of a chess opening?
Paste the moves from the start of the game, a complete PGN, or a full FEN. The finder compares the line and resulting position with its ECO opening reference, then returns the opening name, variation and code when it finds a match.
What is an ECO code?
ECO stands for Encyclopaedia of Chess Openings. Its five groups, A through E, divide named openings into codes from A00 to E99. A code covers a family, while the variation name identifies a more precise line.
Does the finder recognize transpositions?
Yes, when the entered line or FEN reaches a position in the reference. A transposition reaches the same chess position through a different move order. The result says when it used a position match instead of a direct move-sequence match.
Why does a FEN sometimes have more than one opening name?
FEN records a position, side to move, castling and other game state, but it does not preserve the move history. Some positions belong to more than one named move order, so the finder can show additional names attached to the same position.
Turn the opening into work you can keep
Build replies in the free repertoire builder, compare the line with your games in the Explorer, or save variations and notes in a Study.