81Sudoku
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Last updated: July 30, 2026
81Sudoku ("81Sudoku", "we", "the site") is a small, independently run Sudoku game at 81sudoku.com. This page explains what data we collect when you use the site, why we collect it, and how you can have it deleted. We don't sell your data, and we don't use it for advertising - there's no ad network on this site, and no third-party analytics or tracking scripts of any kind. We do keep an anonymized daily visitor count to understand overall site usage - see "Anonymous Visit Counts" below for exactly how that works.
We collect different data depending on how you use the site:
If you're signed in, we set a session cookie so the site knows you're logged in - this is required for accounts to work and isn't used to track you across other sites. If you play without an account, your in-progress puzzle and settings are kept in your browser's local storage rather than on our servers, so they stay on that device. We don't set any cookie, local storage entry, or other data on your device to count visits - the mechanism below runs entirely on our server - so there's no tracking cookie, advertising cookie, or cookie-consent banner here.
To understand roughly how many people use the site day to day, each logged-out page load is turned into a one-way hash of your IP address, browser type, and the current calendar date, combined with a secret value that only our server holds. We store that hash, not your IP address. Because the calendar date is baked into the hash, the same visitor gets a completely different, unrelated hash every day - there's no way to link one day's visit to the next, or to build a profile of you over time. This is used only to count roughly how many distinct people visit each day; it's never linked to an account, and rows older than about 35 days are deleted. This particular visit count only covers logged-out visits - signed-in activity is already covered by your account activity above.
Separately, and using this same one-way hashing approach, we also record a best-guess classification of the pointing device you're using that day - mouse, trackpad, or touch screen - based on how you interact with the page. Unlike the visit count above, this runs for signed-in sessions too, since it's purely aggregate input-device statistics and isn't linked to your account or identity in any way. Same retention (about 35 days) and same hash-based, non-reversible storage.
We use two outside services, and nothing else:
We don't share, sell, or rent your data to anyone beyond these two processors, and we don't run any third-party analytics or advertising scripts. The anonymous visit count described above runs entirely on our own server - no outside service ever sees it.
We keep account and gameplay data for as long as your account exists. Feedback submissions are kept until we no longer need them for their stated purpose (following up on feedback), or until you ask us to delete them. Anonymous visit hashes are kept for about 35 days, then deleted automatically.
There's currently no self-service "delete my account" button in the app. If you'd like your account and associated data deleted, or have a feedback submission removed, email [email protected] and we'll take care of it.
81Sudoku is a small, actively developed project, so this policy may be updated as the site changes. We'll update the "Last updated" date above when it does.
Questions about this policy or your data can be sent to [email protected].