MathCastle
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Privacy

Last updated 16 September 2026

MathCastle collects as little as it can. This page lists everything the site stores and why.

Without an account

  • On your device. Your practice record (which problems you got right or wrong, lessons completed, flashcard schedule, streak, XP, settings and the name shown on leaderboards) lives in your browser's local storage. It never leaves your device unless you sign in. Clearing site data removes it.
  • Anonymous attempt log. When you answer a problem, the site records that some user answered that problem correctly or incorrectly, how long it took, and where (practice, a game, a lesson). No account, name, IP address or device identifier is stored with it. It is used only to recalibrate problem difficulty.
  • Problem reports. If you report a problem, the report text and the answer you entered are stored so an editor can fix the problem. Reports are not linked to you.
  • Game scores. Scores you post to the leaderboards are stored with the board name you chose.
  • Error reports. If the site crashes in your browser, the error message, the page address and your browser's user-agent string are logged so the bug can be fixed. Nothing you typed is included.

With an account

  • Your name, email address and a salted hash of your password (or, for Google sign-in, the identifier Google provides). We do not store Google passwords or contacts.
  • The same progress record described above, synced to the server so it follows you between devices. It is readable only by you.
  • Leaderboard scores are credited to your account instead of a typed name.

What we do not do

  • No advertising, no ad networks, no third-party analytics or tracking scripts.
  • No selling or sharing of data with anyone.
  • No cookies other than the session cookie that keeps you signed in.

Children

MathCastle is used by students from Grade 4 upward. No account is needed to use any part of the site, and an account stores only a name and email address. A parent or guardian can ask for an account and its data to be deleted at any time.

Deleting your data

Without an account, clear the site's data in your browser. With an account, use Settings to delete the account, which removes the account and every synced progress record.

Hosting

The site runs on Vercel with a Neon Postgres database in the United States. Both are covered by their own security policies.