Chess Analysis Board
Paste any position as a FEN string and a Stockfish engine running inside your own browser will tell you the best move, the evaluation and the full line — including the solution to a mate-in-2 puzzle.
How to use this board
- Paste a FEN into the box on the right and press Load position. The board redraws instantly.
- Press Analyse. Stockfish starts thinking and the depth counter climbs. The evaluation and the best move update as the search gets deeper.
- Click any move in the line the engine shows to play the position forward on the board, then press Undo to step back.
- You can also just drag pieces by clicking a square and then its destination — the FEN box updates itself after every move.
Solving a puzzle? Paste the puzzle's FEN and press Analyse. If a forced mate exists the engine reports it as Mate in 2 (or 3, or 4) within a second or two, and the line beside it is the solution. This is a proof, not a guess — the engine has searched every defence.
What is a FEN string?
FEN stands for Forsyth–Edwards Notation. It is one line of plain text that stores a complete chess position, which is why every chess site, database and book diagram can exchange positions with it. The starting position looks like this:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
It has six fields separated by spaces:
- Piece placement — the eight ranks from 8 down to 1, separated by
/. Uppercase letters are White pieces, lowercase are Black, and a digit means that many empty squares in a row.
- Side to move —
w or b. Getting this wrong is the most common reason an engine gives a strange answer.
- Castling rights — any of
KQkq, or - if nobody may castle.
- En passant target square — the square behind a pawn that has just moved two squares, or
-.
- Halfmove clock — moves since the last capture or pawn move, used for the fifty-move rule.
- Fullmove number — starts at 1 and increases after each Black move.
Composed problems and puzzle diagrams often end in 0 1 because the position is a starting point rather than part of a real game. That is completely normal and the engine does not mind.
Reading the evaluation
The number at the top of the engine panel is always shown from White's point of view, measured in pawns:
+0.3 — roughly balanced. Anything inside half a pawn is a normal, playable position.+1.5 — a clear advantage for White, usually worth a pawn and a half.-3.0 — Black is up about a piece and should be winning with accurate play.Mate in 3 — no number is shown, because a forced checkmate outranks any material count.
The depth figure below the line is how many moves ahead the engine has searched. Early depths are rough; once the depth stops climbing and the line stops changing, the verdict is stable. For a two-move mate that happens almost immediately.
Why the engine sometimes changes its mind
A search is not a lookup. At depth 12 the engine may like one move, and at depth 20 it finds a defence it had not seen and switches. This is normal and it is exactly why the depth counter is displayed — it tells you how much to trust what you are reading.
♔ Analysis is practice. Playing is progress.
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Frequently Asked Questions
What is a FEN string in chess?
FEN stands for Forsyth-Edwards Notation. It is a single line of text that describes a complete chess position: where every piece stands, whose turn it is, which castling rights remain, whether an en passant capture is available, and the two move counters. Because it is plain text you can copy a FEN from any chess site or book diagram and paste it into an analysis board to recreate the position exactly.
How do I analyse a chess position online for free?
Paste the position's FEN into the box on this page and press Analyse. A Stockfish chess engine runs inside your own browser and returns the best move, a numeric evaluation and the full line it expects both sides to play. Nothing is uploaded to a server and no account is needed.
Can an engine solve a mate in 2 puzzle?
Yes. Paste the puzzle position as a FEN and the engine will report a forced mate as a mate score, for example Mate in 2, together with the exact moves. This is the fastest way to check a composed problem or a daily puzzle when you are stuck, because the engine proves the mate rather than guessing at it.
Does this analysis board send my position to a server?
No. The Stockfish engine is compiled to WebAssembly and runs entirely inside your browser tab. The position you paste never leaves your device, which is also why the board keeps working if your connection drops after the page has loaded.
What does the evaluation number mean?
The evaluation is shown from White's point of view in pawn units. A score of +1.0 means White stands about one pawn better, and -2.5 means Black is about two and a half pawns ahead. Roughly speaking anything inside plus or minus 0.5 is balanced, and an advantage above 2.0 is usually winning with accurate play. When a forced checkmate exists the engine shows a mate score instead of a number.
Why does the engine keep changing its mind?
The engine searches deeper the longer it thinks, and the displayed depth rises as it goes. Early evaluations at low depth are rough; the line usually settles once the depth stops climbing. For most positions a few seconds is enough, and for a mate in 2 the answer appears almost immediately.
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