Find your worst blunder
Enter your username and we scan your recent games — right here in your browser, no account, nothing uploaded. Thirty seconds later you'll know exactly which move to be embarrassed about.
A free chess blunder checker that runs in your browser
Wondering why you keep blundering? Paste a game or enter your username and this blunder checker analyzes your chess games for free — no account, no upload, no waiting in a queue. A real chess engine (Stockfish, compiled to WebAssembly) runs on your own device, replays your recent games move by move, and flags the single biggest eval swing it can confirm at depth: your worst blunder, shown on a board with the move you played in red and the move the engine wanted in green.
Every result is double-checked — a quick pass finds candidate mistakes, then a deeper search confirms the swing before you see it. That's the same standard the full Blunders game analysis uses, where each blunder becomes a training puzzle built from your own play. When you're ready to stop repeating the mistake, the free puzzle trainer has thousands of positions across every tactical theme, the daily puzzle keeps you sharp in one minute a day, and the opening guides cover the lines you actually reach.
The free account needs no credit card — Pro is optional.