Without an account
Progress, code drafts, submissions, notes and preferences are saved only in your browser's storage. They are not sent anywhere unless you sign in or export a backup yourself.
With an account
Signing in with GitHub, Google or an emailed link creates an account with our authentication provider, Supabase. It stores:
- your email address and the basic profile the sign-in provider shares (such as name and avatar), used only to identify your account;
- one copy of your practice data, so it can sync to your other devices.
Each account can read and write only its own copy. It is protected in transit and by access rules but is not end-to-end encrypted, so keep passwords and confidential material out of notes and code. Your sign-in session is kept in your browser and ends when you sign out or 30 days after sign-in.
Running code
Python, JavaScript and TypeScript run in your browser; the Python runtime is downloaded from the jsDelivr CDN. Java, C++ and Go are sent to a server, run in an isolated sandbox without network access, and are not stored.
What we do not do
The site has no ads, analytics or tracking scripts, and your data is never sold or shared. The hosting provider, Vercel, keeps standard request logs.
Removing your data
Delete the cloud copy at any time from Account & sync under Advanced. When signing out, check “Also remove my practice from this browser” to clear this device. To delete the account itself, contact the maintainer through the project repository.