AnalysisFree Chess Analysis Board
Paste a FEN or PGN or play moves. Stockfish 18 runs in your browser: engine lines, eval bar, and game review. No account, no upload.
How to use the chess analysis board
Load a position or a game
Paste a FEN to load one position, paste a PGN to load a whole game with its variations and comments, or play moves on the board from the start position. The board editor lets you set up any position by hand.
Read the engine lines
The engine starts when you play a move, load a game or a position, or switch it on. Stockfish 18 then shows up to five lines with an evaluation and win, draw, and loss percentages. The eval bar tracks the current position. Click a line to play it onto the board and step through it with the arrow keys.
Run game review
Game review checks every move of the game, marks each one from brilliant to blunder, and reports accuracy for both sides, an estimated rating, and an evaluation graph you can click to jump to any moment.
Share or keep playing
Copy the share link to send the position to anyone. The link carries the FEN or PGN, so whoever opens it sees the same board. When you are done, take what you found into a Zapp Chess battle from the Practice tab.
The board works for any game you played or studied. If you are reviewing an opening, the Italian Game, Queen's Gambit, and London System trainers walk through the main lines move by move.
What you get
Engine lines and eval bar
Up to five Stockfish 18 lines with evaluation, depth, and win, draw, and loss odds, plus an eval bar that follows every move.
Game review and accuracy
Every move classified from brilliant to blunder, accuracy for White and Black, an estimated rating, and an evaluation graph.
Board editor
Set up any position: place pieces, choose the side to move, set castling rights, then analyze it or copy the FEN.
Variations and comments
Add side lines from any move, promote a variation to the main line, delete from a move onward, and write comments that stay in the PGN you copy.
PGN and FEN import, share link
Paste a PGN with variations and comments or a FEN, see the opening name and ECO code, and share a link to the exact position.
Board themes and keyboard
The board themes from the Zapp Chess game, arrow-key navigation through moves and variations, and a layout that works on phones.
Paste a FEN or PGN
A FEN is one line of text that describes a single position: the pieces rank by rank from the eighth rank down, the side to move, castling rights, the en passant square, and the move counters. This one is the Italian Game after 1. e4 e5 2. Nf3 Nc6 3. Bc4 with Black to move:
r1bqkbnr/pppp1ppp/2n5/4p3/2B1P3/5N2/PPPP1PPP/RNBQK2R b KQkq - 3 3A PGN holds a whole game: optional header tags, then the moves. Variations go in parentheses and comments in braces, and both load into the move list. Most chess sites and apps export PGN with one click:
1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 (3... Nf6 {Two Knights Defence}) 4. c3 Nf6 5. d4 exd4 6. cxd4 Bb4+ *Paste either one into the input on the board above. The page detects the format, loads it, names the opening with its ECO code, and starts the engine on the current position.
Game review and move classifications
Game review runs Stockfish 18 on every position of the game and compares each move with the engine's best move. The size of the evaluation drop decides the label. Accuracy for each side, an estimated rating, and the evaluation graph are built from the same data.
- brilliant
- A strong sacrifice or a hard-to-find move that gives up material and still keeps the best evaluation.
- great
- The only move that holds the position; every other move would lose ground.
- best
- The engine's first choice in that position.
- excellent
- Almost as good as the best move; the evaluation barely changes.
- good
- A sound move that keeps the position in the same range.
- book
- A known opening move from theory.
- inaccuracy
- A small slip; the evaluation drops a little.
- mistake
- A clear error; the evaluation drops by a meaningful amount.
- miss
- A winning chance skipped: the engine saw a tactic and the move played did not use it.
- blunder
- A serious error that throws away a large part of the evaluation, often a piece or the game.
Works in your browser
The engine runs as a WebAssembly worker inside your browser tab. Your positions and games stay on your device: nothing is uploaded, there is no account, and no history is stored on a server. The share link carries the FEN or PGN inside the URL itself.
The first visit downloads the engine once, about 5.6 MB, and the browser caches it. After that the board loads fast, and analysis speed depends only on your device. Phones get a shallower search than laptops, but the same evaluations.
Engine: Stockfish 18, the Stockfish.js WebAssembly build of Stockfish, used under the GNU GPL v3 license. The Stockfish project is not affiliated with Zapp Chess.
FAQ
Is the chess analysis board free?
Yes. The analysis board, engine lines, game review, and board editor are free with no daily limit and no account. The Stockfish 18 engine runs inside your browser, so there is no server queue and nothing to unlock. The only download is the engine itself, about 5.6 MB, which your browser caches after the first visit.
Which chess engine does the analysis board use?
It uses Stockfish 18, the strongest open-source chess engine, compiled to WebAssembly by the Stockfish.js project. The build is the single-threaded lite NNUE version, so it works on phones and laptops without special settings. It shows up to five engine lines with an evaluation and win, draw, and loss percentages for the position on the board.
How do I analyze a game from chess.com or lichess?
Export or copy the game as PGN from the site where you played it, then paste the text into the PGN box on this page. The moves, variations, and comments load into the move list. Click any move to see the engine evaluation at that point, or run game review to classify every move and get an accuracy score for each side.
What is a FEN in chess?
FEN (Forsyth-Edwards Notation) is a one-line text description of a chess position: the piece placement rank by rank, the side to move, castling rights, the en passant square, and the move counters. Paste a FEN here to load that exact position and analyze it. You can also set up a position in the board editor and copy its FEN.
What is a PGN file?
PGN (Portable Game Notation) is the standard text format for a chess game: optional header tags such as the player names and the result, followed by the moves in algebraic notation. It can hold variations in parentheses and comments in braces. This analysis board reads all of that, keeps the variations in the move list, and lets you add your own.
What do the evaluation numbers and the eval bar mean?
The evaluation is the engine's estimate of the position in pawn units from White's point of view: +1.5 means White is about a pawn and a half better, -0.3 means Black is slightly better, and M5 means a forced mate in five moves. The eval bar shows the same number as a white and black share of the bar, so you can read the balance at a glance.
How does game review work?
Game review runs the engine on every position of the game and compares each move with the engine's best move. The size of the evaluation drop decides the classification, from brilliant to blunder. The tool then totals the results into an accuracy percentage for each side, an estimated rating, and an evaluation graph you can click to jump to any move.
What do the move classifications mean?
Best is the engine's top move, and excellent or good are close to it. Book marks a known opening move. An inaccuracy loses a little, a mistake loses a clear amount, and a blunder throws away a lot, often a piece or the game. A miss means you skipped a winning chance, great marks the only move that holds, and brilliant is a strong sacrifice.
Can I set up any position with the board editor?
Yes. The board editor lets you place or remove pieces on any square, choose the side to move, set castling rights, and clear or reset the board. When the position is legal you can analyze it, play it out against the engine, or copy its FEN and share link. This is useful for positions from books, puzzles, or a board at home.
Does the analysis upload my games to a server?
No. The engine runs as a WebAssembly worker inside your browser tab, so the positions and games you analyze never leave your device. There is no account, no login, and no history stored on our side. The share link only encodes the FEN or PGN in the URL, and only the people you send it to can open it.
Practice what you found in Zapp Chess
Zapp Chess battles start from real mid-game positions and last a handful of moves, so the tactics you spot here come up again in minutes, not hours. Play in the browser or on your phone.