Legal

Privacy

Effective 6 August 2026

Local use

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.

Signed-in sync

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.

Other requests

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.

Control and retention

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.

Contact and changes

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.