Analyze Your Chess Game

Chess Game Analysis, Right in Your Browser

Every game you play has something to teach you, but only if you go back and look. This page is the going back. Paste the PGN of a game - from Chess.com, Lichess, a database, a club tournament, or one you typed out yourself - and Stockfish 18 at Skill Level 20 searches every single position in it. You get the move you played, the move the engine wanted, and an honest number for the gap between them.

Every position gets a fixed slice of the engine's time rather than a fixed depth, because a fixed depth is cheap in a sharp position and far too cheap in a quiet one - and quiet positions are exactly where a shallow search gets the evaluation wrong. Standard gives each position half a second, which is around forty seconds for a forty-move game; Quick spends a fifth of a second, and Deep spends 1.2 seconds. Hover the Game report heading and it will tell you the depth that budget actually bought.

Nothing is uploaded. The engine is compiled to WebAssembly and runs on your own machine, which is why there is no per-game limit, no queue and no account needed. It also means a long game on a slow phone takes a while; pick Quick if you are in a hurry, or Deep if you want the engine to be sure.

How Each Move Is Graded

Raw centipawns are a poor way to judge a move. Dropping 200 centipawns when you are up a queen barely matters; dropping the same 200 in a level middlegame can lose the game outright. So every position is first converted to a winning chance between 0% and 100%, and each move is graded by how much of that chance it gave away.

What The Report Shows

The report opens with the two players and how it ended for each of them - won, lost or drew - and the opening the game came out of. Under that is a count of every grade for both colours side by side, so you can see at a glance whether the game turned on a single blunder or leaked away slowly. Missed wins sit in the same table, because a won game let go is worth knowing about even when no individual move looks especially bad.

There is no accuracy percentage and no rating estimate. One game is far too small a sample for either to mean much, and a quiet game flatters you while a sharp one punishes you for the same standard of play. What is left is the thing you can act on: which moves were errors, how bad each one was, and what should have been played instead. If you want a rating figure across several games, Estimate My ELO is built for that.

Practise The Mistakes, Not Just Read Them

Reading that you blundered on move 24 changes nothing by itself. Every grade that actually happened carries its own practice button directly under its count, so you can work through just the blunders, or just the missed wins, rather than everything at once. A grade you avoided shows no button at all - no blunders in the game, no blunders drill.

Each exercise puts you back in the position with the clock wound back and the board exactly as it stood, and draws the move you actually played on it in that grade's colour. You are not being asked to remember what went wrong; you are being asked to find what should have gone right.

Your answer is then searched by the engine rather than compared against a stored solution. That matters, because most positions have more than one good move: anything that holds the evaluation is accepted, not just the one line the review happened to pick. The check gets at least a full second of Stockfish at Skill Level 20 on that exact position, and never less than the sweep that found the mistake in the first place - this is the moment the answer has to be right.

There is a hint if you need one, unlimited retries, and once you have found the move you can carry on playing the position out against Stockfish. That last part matters more than it looks: plenty of players spot the right move in a puzzle and still fail to win the position afterwards, and playing it out is the only way to find that out.

What The Board Is Telling You

• The coloured arrow is the move that was actually played, tinted by its grade.
• The gold arrow is what the engine wanted instead. It only appears when the move you played gave something away.
• The stamp on the destination square is the grade for that move.
• The bar beside the board is the evaluation, always from White's side: white filling upward means White stands better.
• Key moments collects the handful of moves that actually decided the game - click one to jump straight there.
• Look deeper re-searches whatever position you are looking at for several seconds and lists the engine's top three lines from it.

Pulling Your Games In By Username

You do not have to go and find the PGN yourself. Type your Chess.com or Lichess username, press Import recent games, and your last twenty standard games appear with the opponent, the date and how it went. Click one and the review starts there and then - and because the site already told us which colour you had, the report and the practice drills are pointed at your side automatically.

Only the username is needed. There is no password to give, no account to connect and no permission to grant, because both sites publish finished games openly for anyone to read. Your browser asks them directly and the games never touch our server. Variants such as Chess960 are filtered out - the review expects standard chess.

Which PGNs Work

Anything sensible. Headers are optional, clock comments such as {[%clk 0:03:00]} and engine annotations are stripped, sidelines in brackets are ignored, and a file holding several games gives you a picker. A game that starts from a set-up position works too as long as the PGN carries its FEN header. If a move cannot be read the review stops there and tells you which one, rather than refusing the whole file.

Frequently Asked Questions

How do I analyze a chess game from a PGN? Copy the PGN, paste it into the box at the top of this page and press Analyze Game. Stockfish searches every position and reports the best move, the move played, and the difference.

Can I analyze my Chess.com or Lichess games by username? Yes. Type your username, press Import recent games, and your last twenty standard games appear with the opponent, date and result. Click one and the review starts immediately — no password and no account connection needed.

What counts as a blunder? A move that gives away 30 percentage points or more of winning chance compared with the best move available. Twenty points is a mistake, ten is an inaccuracy. Once a game is decided the percentages stop separating the moves, so from three pawns ahead or behind the material a move costs is graded too - five pawns is a blunder, two and a half a mistake, and a little over one an inaccuracy.

How is the game review run? The engine runs directly in your browser using WebAssembly, analyzing your moves locally on your device.

What does Practice My Mistakes do? Each kind of error gets its own drill. It puts you back in the position with your move drawn on the board and asks for the one you should have found; the engine checks your answer, so any move that holds the position is accepted.

How deep does it actually search? As deep as the budget buys. Half a second of Stockfish 18 is usually depth 17 to 20 on a laptop and rather less on a phone, so the review measures what it managed rather than promising a number - hover the Game report heading and it will tell you the typical and the shallowest depth the run reached. If a position comes up short of a sensible minimum the search is extended until it gets there.

Why does it not give me an accuracy percentage? Because a single game does not support one. The figure swings on how sharp the game happened to be rather than how well you played, and it invites comparison across sites that all calculate it differently. The grades and the drills are what actually tell you something.

When you are ready to put it into practice, go and play chess against Stockfish, sharpen the patterns with chess puzzles, get live AI chess coaching as you play, or take an estimate of your ELO rating.