Deblunder study notebook
How Deblunder works: from your games to a training plan
Deblunder is an independent web app for studying completed chess games. It reads your games from Chess.com, Lichess or PGN, finds causes of mistakes that repeat, explains them on the board and trains them with your own positions in Portuguese or English.
1. Connect your games
You connect Chess.com or Lichess with your public username, or upload PGN files. Deblunder never asks for your platform password and is not affiliated with Chess.com or Lichess. Rapid is the default time control; Blitz, Bullet or all together are available, and ratings from different time controls or platforms are never mixed.
Preparation analyzes up to 10 games in the chosen time control and can expand to 30. Later syncs bring only new games.
2. Diagnosis: causes, not just labels
Each game is analyzed with Stockfish. Deblunder then looks for the board relation that explains a mistake: a piece that was defending or blocking, a check that was not considered, a line that opened. When the board proves the cause, it shows it with pieces and lines. When it cannot, the mistake stays marked as an unknown cause instead of receiving an invented explanation.
A pattern only appears when the same cause repeats in different games. Priorities come from the whole analyzed sample, and the sample size is always visible.
3. Training in four steps
Training uses positions from your own games in short sessions of 3, 5 or 10 positions. Each position goes through Solve, Understand, Compare and Recall. In Solve and Understand the engine answer stays hidden; Compare is where you explore alternatives; Recall hides the answer again in later reviews.
Only the first valid attempt is scored. Practice attempts never change your accuracy or the dates of spaced reviews, so the numbers reflect what you actually found on your own.
4. Observed evolution
After you play new games, Deblunder shows whether the causes you trained appear less often, with the sample in view. Game evidence and training evidence are shown separately.
This is observation, not a promise. Deblunder does not guarantee rating gains and does not work during a game: it only analyzes finished games, for study between games.
Price and access
Creating an account, connecting games, seeing the diagnosis and completing the first training are free, without a card. After that, full access is paid: a direct subscription, or a 7-day trial before the first charge. Prices depend on the country and are shown on the official site.
Cancellation takes one click in your account. Your games, diagnoses and training history stay saved to view and export.
Frequently asked questions
What is Deblunder?
Deblunder is a web app that turns your own completed chess games into a diagnosis of recurring mistakes and personalized training. It supports Chess.com, Lichess and PGN, in Portuguese and English.
Who is Deblunder for?
Players who play online regularly and want to know why they keep losing points in the same way, and who prefer short, regular training with their own positions over generic study.
Does Deblunder replace Chess.com or Lichess?
No. You keep playing where you play. Deblunder is a study tool that uses your completed games from those platforms or PGN.
Is my data private?
Deblunder reads public game data through your public username or the PGN files you upload. It does not need platform passwords. The privacy policy on the official site describes how account data is handled.