Privacy Policy

Last updated: 10 June 2026

The short version. Sudoku is built to need almost nothing from you. There are no accounts, no logins, and no email or name. Your games, settings, streak, and stats live only on your own device. The single thing that ever leaves your device is your daily challenge completion time, sent with a random anonymous ID so we can show you a rank — and you can wipe that ID at any time by clearing your browser data.

Who we are

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

No account, ever

The app is anonymous-first. We do not ask you to register, sign in, or provide any personal details such as your name, email address, phone number, or date of birth. There is no user profile.

Data stored on your device (and only your device)

Almost everything the app remembers is kept in your browser’s localStorage on your own device. It is never transmitted to us. This includes:

Settings — theme (light/dark), mistake-checking, auto-clean notes, haptics.
Your current game — the puzzle and your progress, so you can close the app and resume later.
Stats — games played, win rate, and best/average times per difficulty.
Daily streak — your current and best streak and the dates you completed.
Campaign / Mini progress — levels completed and stars earned.
An anonymous device ID — a random identifier (see below).

You can erase all of this at any time by clearing your browser’s site data for this app, or by uninstalling the installed app. Doing so resets the app to a brand-new state.

The one thing that leaves your device: daily challenge times

The Daily Challenge has an optional leaderboard. When you complete the daily puzzle, the app sends to our server:

the puzzle date (e.g. 2026-06-10),
your completion time in milliseconds, and
a random anonymous ID (an automatically generated token, e.g. a random UUID) stored on your device.

That is the entire record. It is not linked to your name, email, IP address, or any other identity — the random ID is the only key. We use it to rank that day’s times and to enforce one ranked attempt per device per day. We do not send your puzzle solution, your other stats, or anything else. If you never finish a daily challenge, nothing is ever sent.

Because the ID is random and unlinked to you, clearing your browser data generates a fresh ID and effectively detaches you from past entries. We cannot identify or contact you from a stored time, which also means we cannot single out and delete “your” specific rows on request — but you can always sever the link yourself by clearing site data.

Fetching the daily puzzle

To fetch the canonical daily puzzle, the app makes a simple request to our server (/api/daily). This request carries no identifier from you. As with any internet request, our hosting provider receives standard technical information (such as your IP address) needed to deliver the response — see “Hosting” below.

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 and reliably, as is normal for any website. Anonymous daily times are stored in Cloudflare’s D1 database; the daily puzzle is cached in Cloudflare KV (and expires automatically after about two days). See Cloudflare’s Privacy Policy.

Advertising

The current version of the app shows no real advertising and includes no advertising or tracking SDK — ad slots are non-functional placeholders. If advertising is introduced in a future version, it will be limited to a banner outside the puzzle and an opt-in rewarded ad you choose to watch; ads will never cover the board or interrupt a puzzle. Should a third-party ad network (for example Google AdSense or AdMob) be added later, it may collect data under its own privacy policy, and this page will be updated to disclose it before such ads go live.

Analytics and tracking

We use no analytics, no tracking pixels, no fingerprinting, and no third-party cookies. We do not sell or share personal data, because we don’t collect data that identifies you.

Cookies

The app does not use cookies for tracking. It uses your browser’s local storage only to keep the app working (settings, saved game, the anonymous daily ID described above).

Children’s privacy

Sudoku is suitable for all ages and does not knowingly collect personal information from anyone, including children. Since no accounts or personal details are collected, the app does not gather data that could identify a child.

Your choices

Reset everything: clear this site’s data in your browser settings, or uninstall the installed app.
Skip the leaderboard: simply don’t complete the daily challenge, and no time is ever submitted.
Offline play: regular and campaign puzzles are generated on your device and work with no network connection at all.

Changes to this policy

If this policy changes, we will update the “Last updated” date above. For any material change (such as adding a real ad network or analytics), the page will be revised before that change takes effect.

Contact

Questions about privacy? Email chiselinkapps@gmail.com.