Free tool
Chess blunder checker
Most blunder checkers scan one game and move on. Audit Chess finds the blunders across your whole history with Stockfish, shows you the ones you make again and again, and turns them into puzzles you can actually practise - so you stop repeating them. Free, in your browser, no account.
Try it: a puzzle built from a real blunder
This is the real board, running Stockfish in your browser. Find the move that was missed in an actual game - exactly what a blunder puzzle looks like once Audit Chess extracts it from your history.
From detection to practice, not just a list
A blunder checker that only labels your mistakes tells you what already went wrong. The harder problem is not seeing a blunder after the game - it is not making it again. Audit Chess is built around that second problem: every blunder and missed tactic from your real games becomes a Stockfish-verified puzzle that drops you back into the exact position you got wrong.
Puzzles come in two flavours. A FIX puzzle is a position where you went wrong - find the move you missed. A PUNISH puzzle is a position where your opponent blundered and you failed to cash in - find the refutation. Both are graded live by the engine, so you are never rewarded for a plausible-but-wrong idea.
The blunders you repeat matter most
A one-off blunder is noise. The same blunder in the same structure, three games in a row, is a lesson. Because Audit Chess analyses your whole Lichess or Chess.com history at once, it can surface the patterns a single-game checker never sees: the recurring tactical oversight, the winning positions you keep throwing away, and the forced mates you keep missing.
For a deeper walk-through, read how to stop blundering in chess and the difference between an inaccuracy, a mistake and a blunder.
Check one game, or your entire history
Want to check a specific game right now? Paste its PGN into the free analysis tool and every mistake and blunder is flagged move by move. Want the bigger picture? Enter your username on the main analysis page and Audit Chess reviews every game, ranks where your points go, and builds your blunder puzzles automatically.
Frequently asked questions
How do I check my chess games for blunders?+
Audit Chess reviews your games move by move with Stockfish and flags every inaccuracy, mistake and blunder - the moves where your evaluation dropped sharply. To check a single game, paste its PGN into the free analysis tool; to check your whole Lichess or Chess.com history at once, enter your username.
What counts as a blunder?+
A blunder is a move that hands over a large, usually decisive advantage - a big swing in the engine evaluation against you. Smaller drops are labelled mistakes and inaccuracies. Audit Chess uses win-probability swings on a Stockfish evaluation to classify each move.
Can it find the blunders I make repeatedly?+
Yes - that is the point. Instead of listing blunders one game at a time, Audit Chess looks across your whole history to surface the mistakes you keep repeating: the same tactic you miss, the same square you weaken, the winning positions you throw away.
How do I actually stop blundering?+
Audit Chess turns your real blunders into puzzles. Each one drops you into the exact position you got wrong so you can find the move you missed (FIX) or punish an opponent who blundered (PUNISH), with Stockfish verifying every solution. Drilling your own mistakes is far more efficient than random puzzles.
Is the blunder checker free?+
Yes. It runs entirely in your browser using Stockfish, needs no account, and nothing is uploaded.
Audit Chess is free and not affiliated with Chess.com or Lichess.