Privacy Policy

Last updated: 17 July 2026

The short version. Sudoku plays fully anonymously — no sign-up is required, and your games, settings, streak, and stats live on your own device. A few things are optional: an anonymous leaderboard (a random ID + your times, and a nickname if you set one), signing in with Google to sync your progress across devices and add friends, and, in the Android app, ads (opt-in "watch to earn" rewarded ads) served by Google AdMob, which uses your device's advertising ID. You can delete your account and data at any time — see “Deleting your account and data.”

Who we are

This Privacy Policy covers the Sudoku app at sudoku.chise.link and its installed (Progressive Web App / Google Play) versions, collectively “the app.” The app is operated by the developer reachable at chiselinkapps@gmail.com.

Anonymous by default

You can install and play the entire game without an account, a login, or any personal details. Regular and campaign puzzles are generated on your device and work fully offline. The features below (accounts, the leaderboard, friends, ads) either activate only if you choose them or collect only anonymous data.

Data stored on your device

Almost everything the app remembers is kept in your browser’s localStorage on your own device and is never transmitted to us. This includes your settings, your current game, your stats, your daily streak, your campaign / mini progress, your XP / level / achievements, your chosen cosmetics, and a random anonymous ID (see below). Clearing this site’s data, or uninstalling the app, erases all of it.

Anonymous leaderboard

The Daily Challenge and the points board are ranked anonymously. When you complete a qualifying puzzle (and you’re online), the app sends to our server:

a random anonymous ID — an automatically generated token stored on your device, not linked to your name, email, or IP address;
your results — the puzzle date and your completion time, and points earned from daily / mini / endless wins;
an optional nickname, only if you choose to set one for the leaderboard.

We use this to rank times/points and to limit ranked attempts per device. We do not send your puzzle solutions or your other stats. If you never finish a ranked puzzle, nothing is sent.

Optional Google sign-in and cross-device sync

You may optionally sign in with Google to keep your progress across devices and to add friends by email. If you do, we receive and store your Google account identifier and email address, linked to your anonymous ID, and we sync your game progress (such as XP, stars, streak, stats and best times) to our server so another signed-in device can restore it. If you never sign in, none of this happens and no email is collected. You can sign out at any time in Settings, and delete this data as described below.

Friends

If you add friends, the app uses a friend code (and, once signed in, your email) so you and a friend can connect and see each other on the leaderboard. Friends you add are stored with your account and removed when you delete it.

Advertising (Android app)

The Android app shows ads through Google AdMob. Ads are limited to opt-in rewarded ads that you choose to watch (for example to get an extra hint or to continue after mistakes); there is no banner over the board and no interstitial that interrupts a puzzle. To serve, measure, and protect these ads, Google’s Mobile Ads SDK collects and shares with Google your device’s advertising ID, IP address, ad interactions, and diagnostic information, for advertising, analytics, and fraud-prevention purposes. This data is handled by Google under Google’s Privacy Policy; see also How Google uses information from sites or apps that use its services. You can reset or delete your advertising ID in your device’s settings, and in the EEA/UK you’ll be asked for consent before personalized ads are shown. The web version of the app shows no ads.

Hosting and infrastructure

The app and its small API run on Cloudflare Pages and Cloudflare’s developer platform. Cloudflare processes standard server request data (including IP addresses) on our behalf to serve the site securely, as is normal for any website. Anonymous leaderboard data, accounts, and synced progress are stored in Cloudflare’s D1 database; the daily puzzle is cached in Cloudflare KV. See Cloudflare’s Privacy Policy.

Analytics and tracking

We run no analytics of our own, no tracking pixels, and no fingerprinting, and we do not sell your personal data. The only third-party that receives data is Google AdMob, and only in the Android app, as described under “Advertising.”

Children’s privacy

Sudoku is not directed to children. Because the app can show ads that use an advertising identifier, it is intended for a general (teen and older) audience and is not designed for children under 13. We do not knowingly collect personal information from children.

Deleting your account and data

You are always in control of your data:

On-device data: clear this site’s data in your browser, or uninstall the app, to erase everything stored locally.
Account & server data: if you signed in with Google or appear on the leaderboard, you can request deletion of your account and associated server data (your Google link and email, synced progress, leaderboard entries and nickname, and friends). See Delete your account and data, or email chiselinkapps@gmail.com.
Advertising ID: reset or delete it in your device’s settings.

Changes to this policy

If this policy changes we will update the “Last updated” date above, and for any material change we will revise the page before that change takes effect.

Contact

Questions about privacy? Email chiselinkapps@gmail.com.