Free Chess Analysis Board
Paste a FEN or a PGN, or set up any position, and Stockfish — running inside your own browser — shows the best move, the evaluation and the top engine lines.
How to use the analysis board
- Load a position or a game. Open the Position tab and paste a FEN or a PGN, then press Load. You can also press Edit board and place the pieces by hand, or simply make moves on the board.
- Let the engine search. With Auto switched on the engine starts by itself after every move. Otherwise press Analyse. The depth counter climbs while Stockfish searches.
- Read the result. The big number is the evaluation from White's point of view, the green arrow is the best move, and each engine line shows how play is expected to continue.
- Explore the lines. Click any move in an engine line to play it on the board, then use the arrow buttons or the left and right keys to step back and forward.
- Save or share. Copy the FEN, copy or download the PGN, or copy a link that opens the same position for someone else.
Pieces move two ways: drag and drop, or tap a piece and then tap its destination. Legal destinations are marked with dots. When a pawn reaches the last rank you are asked which piece to promote to.
Solving a puzzle? Paste the puzzle's FEN and let the engine run. If a forced mate exists it is reported as Mate in 2 (or 3, or 4) within a second or two, and the first engine line is the solution. This is a proof, not a guess — the engine has searched every defence.
Analyse your own game (PGN)
A PGN (Portable Game Notation) is the text record of a whole game — the moves, and usually the players and the result. Almost every chess site lets you copy or download it after a game. To review a game here:
- Copy the PGN of the game from the site or app where you played it. A plain list of moves such as
1. e4 e5 2. Nf3 Nc6 works too.
- Open the Position tab, paste it into the box and press Load. The board jumps to the start and the full game appears in the Moves tab.
- Step through with →. Watch the evaluation bar: a sudden swing is the moment somebody made a mistake.
- At that moment compare the move that was played with the engine's best move, and click through the engine line to see why it is better.
You can play a different move at any point. The board then follows your new move and drops the old continuation, so reload the PGN if you want the original game back.
Set up any position
No FEN to paste? Press Edit board in the Position tab. A palette of pieces appears under the board: pick one and tap the squares where it belongs. Choose whose move it is, tick the castling rights that still apply and press Done.
The board checks the position before it is handed to the engine. Each side needs exactly one king, pawns cannot stand on the first or last rank, and the side that has just moved cannot be left in check. If something is wrong you are told what to fix.
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. If you paste only the first field, or leave the two counters off, the board fills in the rest for you.
Reading the evaluation
The number at the top of the engine panel is always shown from White's point of view, measured in pawns:
| Evaluation | What it means |
|---|
0.00 to ±0.5 | Roughly balanced. A normal, playable position for both sides. |
+1.5 | A clear advantage for White, worth about a pawn and a half. |
-3.0 | Black is up about a piece and should be winning with accurate play. |
Mate in 3 | A forced checkmate. No number is shown, because mate outranks any material count. |
The evaluation bar beside the board shows the same thing as a picture: the larger the white part, the better White stands. The depth figure is how many half-moves ahead the engine has searched. Early depths are rough; once the depth stops climbing and the line stops changing, the verdict is stable.
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. For a hard position, raise the thinking time in Settings.
Engine lines explained
By default the engine shows one line: its best move and the reply it expects to each move after that. In Settings you can ask for 2, 3 or 5 lines. The engine then shows its best few moves side by side, each with its own evaluation.
- If the first line is far ahead of the second, there is only one good move — the kind of position where a tactic must be found.
- If the lines are within a few tenths of a pawn, the position is a matter of taste and several plans are fine.
- More lines cost search depth, because the engine has to prove several moves instead of one. For puzzles and forced mates, one line is the fastest and most reliable setting.
Stockfish 10 or Stockfish 18?
| Stockfish 10 | Stockfish 18 |
|---|
| Download | Well under 1 MB, ready almost instantly | About 5 MB, once; then cached by your browser |
| Evaluation | Classical hand-written evaluation | Neural network (NNUE) evaluation |
| Best for | Puzzles, forced mates, quick checks, slow connections | Quiet positions, openings and endgames where judgement matters |
Both are far stronger than any human player. Stockfish 10 is the default because it starts immediately on any phone. Switch to Stockfish 18 in Settings when you are on Wi-Fi and want the more accurate verdict; your choice is remembered on this device.
Settings and shortcuts
- Auto — analyse automatically after every move or position change.
- Thinking time — 1, 3, 10 or 30 seconds per position, or keep searching until you press Stop.
- Engine lines — how many candidate moves to show.
- Best-move arrows and board coordinates — switch either off for a clean diagram.
- Board colours and pieces — four colour schemes and four piece sets.
| Key | Action |
|---|
| ← | Previous move |
| → | Next move |
| F | Flip the board |
On a phone, use the four arrow buttons under the board. All settings are stored only in your own browser.
Using an engine to improve
An engine tells you what is best, not why. A few habits make the difference between learning from it and just reading numbers:
- Think first, then check. Go through your game without the engine and write down where you think it turned. Only then switch the analysis on. The gap between your guess and the verdict is the lesson.
- Look for the big swings. A change from +0.3 to +0.1 is noise. A change from +0.5 to -2.0 is a blunder worth understanding.
- Play out the refutation. When the engine says your move loses, play your move on the board and click through its line until you can see the point yourself.
- Do not copy engine moves you cannot explain. A human-friendly move that keeps a +1.0 advantage is often a better practical choice than a +1.4 move that needs ten precise follow-ups.
- Never use an engine during a live game. It is cheating everywhere, including on ChessDada. Analysis is for after the game.
♔ Analysis is practice. Playing is progress.
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Frequently Asked Questions
How do I analyse a chess position online for free?
Open the Position tab on this page, paste the position's FEN and press Load. A Stockfish chess engine runs inside your own browser and returns the best move, a numeric evaluation and the line it expects both sides to play. Nothing is uploaded to a server and no account is needed.
Can I analyse a full game from a PGN?
Yes. Paste the PGN into the box in the Position tab and press Load. The whole game appears in the Moves tab and you can step through it with the arrow buttons or the left and right arrow keys while the engine evaluates each position.
How do I set up a custom position without a FEN?
Press Edit board in the Position tab. Pick a piece from the palette under the board and tap the squares where it belongs, choose which side is to move and which castling rights remain, then press Done. The board checks that the position is legal before the engine analyses it.
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.
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.
What do the multiple engine lines mean?
Each line is one candidate move followed by the play the engine expects after it, with its own evaluation. If the first line is far better than the second there is only one good move. If the lines are close together, several moves are fine. You can choose 1, 2, 3 or 5 lines in Settings.
What is the difference between Stockfish 10 and Stockfish 18 on this board?
Stockfish 10 is a very small download that starts almost instantly and is ideal for puzzles and quick checks. Stockfish 18 uses a neural network evaluation and judges quiet positions more accurately, but it is a download of about 5 MB the first time. You can switch between them in Settings.
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.
Does the analysis board work on a phone?
Yes. On a phone the board fills the width of the screen, pieces move by tapping or dragging, and large arrow buttons under the board step through the moves. The engine runs on the phone itself, so longer thinking times use more battery.
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Last updated: October 8, 2026