Your data stays in your browser

Cookies are sent with every request so the server can answer, and they are HttpOnly: scripts on a page cannot read them. The ones that hold your data are signed by the server, so a changed cookie is rejected.

Your session

Proves you are signed in. Cookie sy_session, for 30 days or until you sign out.

Your account

Only if you created one with a Telegram code: your name, username and a scrambled (scrypt) form of your password, never the password itself. Cookie sy_registered_account, for 30 days from when you made it.

Your study data

Your profile (name, school and year), quiz history and answers, XP, badges, challenges, saved posts, reports you filed and your own question sets. Compressed cookie sy_device_state, for 30 days after it last changed.

An unfinished quiz

The answers so far, so a reload does not lose them. Cookie sy_quiz_draft, until you submit the quiz, or 30 days at most.

Registering

The request for a Telegram code and a count of tries. Cookies sy_registration_challenge and sy_registration_attempts, for 10 minutes.

Your photo

Only if you add one: kept in this browser's local storage for 30 days and never uploaded.

Preferences

Light or dark theme, and whether you closed the banner, in local storage. Neither identifies you.

• Svaeng-Yul's server reads your cookies to answer each request and stores nothing. A running server can hold a copy of your data in memory until it restarts.
• Vercel, which hosts the site, records each request (network address, time, page and browser) in its logs for a limited time.
• Telegram, if you register: you open our bot and send it a start message. Telegram passes that message, with your public Telegram profile, to our server, which replies with your code and keeps none of it. Telegram's own privacy policy covers Telegram.
• An AI model, only when one is connected: asking for a hint sends the question and its four options, not your name or account, to Anthropic. Filing a report sends the question, its answer key and the reason and reference you typed. The status page shows whether a model is connected right now.

There are no analytics, no advertising and no tracking cookies. Other students cannot see your data: the leaderboard shows only your own row beside labelled samples.

• Signed in: open Profile, then Settings, then “Delete data on this device”. It removes everything listed above except your two preferences and signs you out.
• Signed out, or you cannot sign in: clear this site's data in your browser's settings.

Either way it is gone for good: Svaeng-Yul keeps no other copy to restore. A class account itself stays, so you can sign in again and start fresh; an account you created with Telegram is deleted with the rest.

Write to chnailab@gmail.com. If this page changes, the date at the top changes with it.