Map your mistakes.

Pull your Chess.com game history, let the engine find where it went wrong, and turn every slip into a puzzle worth revisiting.

Chess.com username

History to import

Analysis depth

The engine runs in your browser, one position at a time — larger histories take longer. You can cancel mid-run; games already analyzed keep their puzzles.

Puzzle library

No puzzle selected. Head to the to pick one, or set up a practice session below.

Practice session

Practice history

By severity

By label

Recent activity

AI coach settings

Blunder Atlas has no server of its own — the "Hint on strategy" coach note calls Anthropic's Claude API straight from your browser using your own API key. The key is stored only in this browser (never sent anywhere except Anthropic) and each hint costs a small fraction of a cent on your own Anthropic account.

Claude API key

Get a key from the Anthropic Console ↗