Privacy notice

What Blunderbase stores

Your email address, held by Blunderbase’s authentication provider so you can sign in.
The Chess.com username you give Blunderbase.
The completed Rapid and Blitz games of that username, from Chess.com’s public archive: the moves, the result, the ratings, both usernames, the opening, and the link to the game.
What Blunderbase derives from those games: engine analysis, the positions it flags, your review schedule, and your practice attempts.
The reflections you type, and the confidence you pick.
A record of each AI request Blunderbase makes on your behalf, so spending can be capped.
The version of these documents you accepted, and when you accepted them.

Blunderbase does not use cookies for advertising, does not run a third-party analytics script on your training pages, and does not sell anything to anyone.

Where your data goes

Your games and everything derived from them stay in Blunderbase’s database, private to your account.

Blunderbase sends data to an AI provider (Anthropic) in three places, and each one sends something different.

Explaining one position. That request contains only:

the position, as a FEN;
the move you played, in coordinate notation;
the engine’s candidate lines and its classification of the mistake;
the reflection you typed;
a teaching mode derived from the confidence you picked. It is one of three values and each confidence maps to exactly one of them, so picking “sure” or “unsure” is visible to the provider even though the word itself is not sent;
the teaching sentences and candidate labels Blunderbase built from the engine’s own output for this position.

Answering a follow-up question you ask about that same position, at most twice per explanation. That request contains everything in the list above, and also:

the question you typed;
the explanation and the cue Blunderbase already showed you;
on a second question, your first question and Blunderbase’s answer to it.

The periodic progress note, once per coaching cycle. That request contains no moves, no positions and nothing identifying a single game. It contains:

the frozen progress report: the period, games played, wins, losses and draws, your rating at each end of it, opening names and your record in each, and the counts behind the mistake pattern it found;
the full list of measurements Blunderbase can score a cycle on;
the mistake category Blunderbase has already proven, and the candidate plans, evidence sentences, practice sizes, cues and success rules it wrote for that category. The model picks from those; it does not write them;
how many practice sessions you completed in the cycle;
the previous cycle’s outcome, and the numbers that outcome was measured from — not only the verdict.

None of the three contains the game’s moves as a whole, the link to the game, your Chess.com username, your opponent’s username, or your email address. Nothing you write or import is used to train a model.

How long it is kept

For as long as you keep your Blunderbase account. There is no archive of deleted accounts.

Deleting your data

You can delete your account from inside Blunderbase. That deletes your profile, your imported games, and every analysis, review, reflection and session derived from them. It does not delete anything on Chess.com.

If you would rather ask a person, write to johnny.barhouche@gmail.com.

Chess.com data

Blunderbase reads completed games from Chess.com’s public archive, for the username you give it. That archive is open to anyone and Blunderbase never signs in to Chess.com, so it holds no password and cannot check that the username is yours. Blunderbase is not affiliated with Chess.com. Deleting your Blunderbase account does not change anything in your Chess.com account.

Children

Blunderbase is for adults only and is not directed at children. If you believe a child has created an account, write to johnny.barhouche@gmail.com and it will be deleted.

Contact

Questions about this notice, or about your data, go to johnny.barhouche@gmail.com. See also the terms of use.