Privacy

You can use Blunderproof without an account. In that mode, games, engine observations, training attempts, and preferences are stored in your browser. Public Chess.com or Lichess data is fetched only for the username you enter. Stockfish analysis runs in your browser.

If you choose to sign in, Blunderproof copies registered device state to your private account so another device can restore it. We store linked public chess usernames, imported games, engine observations and run provenance, training evidence, plans, and preferences. Clerk processes identity and session data; Neon stores application data; Vercel hosts and serves the application.

Opening Explorer requests send an anonymous chess position to the Lichess explorer. Operational logs may contain request metadata, errors, and coarse performance information, but should not contain your full local backup or secret credentials.

A game you paste as a PGN is read and analysed in your browser and kept on that device only. It is not synced to an account and does not enter your profile. Wrapped fetches the public game records of the username you enter, counts them in your browser, and stores nothing. If you save a share card, the username and the figures printed on that card are sent to our server once so it can draw the image. A calendar reminder is a file or link handed to your own calendar; we do not keep the time you chose anywhere but your browser.

Blindfold results, typed answers, and games stay in the page’s memory until you leave or reload. You can download a game as PGN. These practice results are not synced to your account.

Device data remains until you clear it. Signed-in data remains until you delete the account, after which application rows are removed by database cascade. The Profile page can export device data and, when signed in, a queryable account export. It also provides permanent deletion. Provider-side games are public records controlled by the relevant chess platform, not by Blunderproof.

Blunderproof is operated by Petr Lupínek. For any question about your data, or to exercise a right this notice describes, write to lupinekxbt@gmail.com. Material changes will update the effective date.