Privacy

Without an account

Your progress (lessons completed, exercises solved, review schedule, XP, streak and achievements) is saved in your own browser, in local storage. It never leaves your device. Clearing your browser data, or using the "Reset local progress" link in the footer, deletes it.

With an account

If you choose to sign in, we store:

• your email address and display name;
• a salted hash of your password (never the password itself), or the link to your GitHub account if you sign in with GitHub;
• your session, in a cookie that keeps you signed in;
• a copy of your progress, so it follows you across devices.

Progress already saved in your browser is merged into your account the first time you sign in, so nothing is lost.

What we do not do

• No advertising and no tracking of your behavior across other sites.
• No AI features: nothing you do here is sent to an AI service.
• Code is never run on your behalf: nothing you type into an exercise is executed.
• We do not sell your data. It is shared only with the hosts named below, to run the site.

Where it lives

The site is hosted on Vercel, which keeps standard server logs (such as your IP address) for a short time to run and secure the service, and cookie-free Vercel analytics that count page views and measure speed without identifying you. Account data is kept in a Postgres database hosted by Neon.

Deleting your data

You can delete your account at any time from the account page. That removes your email, your sign-in details, your sessions and your saved progress. Progress stored only in your browser stays there until you clear it.