The short version

Sparring Chess stores what it needs to train you and nothing to sell. There are no advertising trackers and no third-party analytics on this site. You can practice without an account; an account is only needed to keep your progress and to use your own games, lines and repertoire.

If you practice without an account

Everything stays in your browser's local storage on this device:

your settings (board size, sparring level, engine options);
the practices you completed, with their moves and results, so your progress can be shown;
a random identifier created in your browser, explained under "Measuring" below.

Clearing your browser's site data removes all of it.

If you create an account

Account: your email address and name (from Google if you log in with Google), a password hash if you sign up with email, and the dates of your logins.
Training data: your lines, uploaded repertoires, practices and their moves, and your settings. The practices you made on this device before signing up are moved into your account.
Imported games: the public games of the Lichess or Chess.com username you ask us to import.
Lichess connection (optional): an access token that lets us query Lichess opening statistics on your behalf. You can disconnect it from the user menu at any time, which deletes the token.

We use this data to run the service for you. We do not sell it and do not share it for advertising.

Measuring

To know whether the product works, we count a few steps: a visit, a practice started or finished, the sign-up prompt, an account created. Each event is stored with the random identifier mentioned above, the line practiced, whether the screen was a phone or a desktop, and the host of the referring site. We do not store your IP address or your browser's user agent with these events, and nothing is sent to third parties. If your browser sends a "Do Not Track" or "Global Privacy Control" signal, no events are recorded.

Cookies

One session cookie keeps you logged in. There are no advertising or tracking cookies.

Emails

We email you to verify your address, reset your password, and tell you when a games import finishes. New accounts may receive a few reminders about finishing their setup. Emails are sent through Resend.

Services we rely on

Google, if you choose to log in with Google.
Lichess and Chess.com, to import the games of the username you give us, and Lichess for live opening statistics if you connect your account.
Resend, to deliver email.
Google Fonts, to load the typefaces of the site.

The chess engine (Stockfish) runs inside your browser. The positions you analyse are not sent to us.

Your rights

You can ask for a copy of your data, for a correction, or for your account and everything linked to it to be deleted. Write to contact@sparringchess.com from the address of your account and it will be done.