Free tool
Chess blunder analyzer
Finding a blunder is easy - any engine does that. The harder, more useful question is why you keep making the same ones. Audit Chess analyzes the blunders across your whole history as a set: it groups the ones you repeat, shows when in the game they strike, and turns them into puzzles so you can actually stop. Free, in your browser, no account.
Blunders as a pattern, not a list
A per-game checker hands you a list and moves on. That tells you what happened; it does not tell you what to change. A blunder analyzer treats your mistakes as data: across your whole history, which tactic do you miss again and again? Which phase does your accuracy fall off a cliff in? Do your blunders spike once you are winning? Those answers only appear in aggregate - and they are the ones worth training on. If you only need every blunder in a single game flagged, the blunder checker does exactly that.
The expensive blunders have their own names
Some blunders cost more than a pawn. Audit Chess separates out the winning positions you threw away - games you led by +3 and lost - and the forced mates you missed, because those are the swings that decide rated games. Fixing a recurring blown-win habit is often worth more rating than any opening tweak.
Analysis that ends in practice
Every blunder the analyzer finds becomes a Stockfish-verified puzzle built from the exact position you got wrong - a FIX puzzle when you erred, a PUNISH puzzle when an opponent blundered and you let them off. For the theory, read how to stop blundering in chess and the difference between an inaccuracy, a mistake and a blunder. Or widen out to all your weaknesses.
What is Audit Chess?
Audit Chess is a chess analysis platform that reads your Chess.com or Lichess game history and identifies the recurring weaknesses, opening tendencies, blunders, blown wins, missed mates and endgame patterns that are hard to see from a single game. It runs Stockfish in your browser, needs no account, and never uploads your games.
What makes it different: most chess engines analyze one position or one game. Audit Chess focuses on the patterns across your whole history - and turns them into training, so your own blunders become Stockfish-verified puzzles and your weakest openings become concrete things to study.
Frequently asked questions
What does a blunder analyzer do?+
It goes beyond flagging blunders in one game. Audit Chess reviews your entire Lichess or Chess.com history with Stockfish, then analyzes the blunders as a set - grouping the ones you repeat, showing when in the game they happen, and which situations trigger them - so you can see the pattern behind your mistakes, not just a list.
How is this different from a blunder checker?+
A blunder checker verifies whether a given move was a blunder. A blunder analyzer studies your blunders in aggregate to explain them: the recurring tactic you miss, the phase where your accuracy drops, the winning positions you keep losing. If you just want every blunder in one game flagged, use the blunder checker; if you want to understand why they keep happening, use this.
Can it tell me when I blunder most?+
Yes. Because it looks across your whole history it can show patterns a single game hides - for example that your blunders cluster in time trouble, in the endgame, or after you reach a winning position and relax. Those triggers are usually more fixable than any individual move.
How do I stop repeating them?+
Every blunder becomes a Stockfish-verified puzzle built from the exact position you got wrong, so you practise your real recurring mistakes instead of random puzzles. Drilling the specific pattern you keep missing is far more efficient than generic tactics training.
Audit Chess is free and not affiliated with Chess.com or Lichess.