In short
- Kyu Sudoku doesn't ask for a name, email, or account — you're identified only by a random ID generated on your device.
- We store only what the leaderboard needs, plus a private backup of your progress so reinstalling the app gets it back: your device ID, chosen board name, and puzzle stats.
- Ads run through Google AdMob: optional rewarded videos in casual puzzles only, for an extra hint or a second chance after a loss. There are no banner ads. Kyu Sudoku doesn't run its own analytics or crash-tracking SDK; AdMob's SDK does some of that incidentally as part of serving ads — see Ads below.
- Daily reminders, if you turn them on, are scheduled entirely on your device — no server ever knows whether you've enabled them.
- If you buy Kyu Supporter, Apple or Google handles your payment directly — we only ever see whether the purchase succeeded.
What we collect
Kyu Sudoku has no sign-up. The first time it runs, it generates a random device ID and stores it on your device. On iPhone a copy also goes in the Keychain, which keeps it when the app is deleted, so reinstalling brings back the same player. That ID — not you by name — is what the leaderboard is built on.
| Data | What it is | Why we collect it |
|---|---|---|
| device_id | A random identifier generated on-device (not your Apple/Google advertising ID) | Ties your stats and leaderboard rows together across sessions |
| display_name | An auto-assigned name like "Player4821," editable by you, shown publicly on the leaderboard | So other players can tell rows apart |
| puzzle stats | Puzzles solved, streaks, best and average times, perfect runs, badges earned, and which daily challenges you've finished | Powers your public profile, and a private backup that restores your Stats screen and badges if you reinstall the app. Only your device can read the backup; nothing public shows it. |
| daily submissions | Your completed board and elapsed time for that day's challenge — only when a run counts (not "off the record" runs) | Verifies a legitimate solve for the daily leaderboard |
| supporter status | Whether you've purchased Kyu Supporter | Shows the supporter mark on your profile and leaderboard row |
What we don't collect
No account means there's a lot we simply never ask for:
Kyu Sudoku itself doesn't run its own analytics or crash-tracking SDK, and never asks for your location. Google AdMob's SDK, as part of serving ads, does incidentally collect some coarse-location and performance/crash data on its own infrastructure — see Ads.
How it's used
Everything in the table above exists for two things: the daily leaderboard with the public profile that comes with it (your rank, streak, and badges), and the private backup of your progress, which is read only when a reinstalled app on your device asks for it. Nothing else about how you play — your settings, saved games, or moves — leaves your device.
Purchases
Kyu Supporter is a one-time, optional purchase with no gameplay effect — just a small mark on your profile. Payment is handled entirely by the App Store or Play Store; Kyu Sudoku never sees your card number, billing address, or any other payment detail. We only receive a yes/no signal that the purchase went through, via RevenueCat.
Ads
Kyu Sudoku shows no banner ads. The only ads are optional rewarded videos through Google AdMob, in casual puzzles only: you can choose to watch one for an extra hint, or for a second chance after a loss. Nothing makes you watch one; there's a free per-puzzle hint allowance either way, set in Settings, that doesn't need an ad at all. The Daily Challenge never grants hints, ad-watched or otherwise — that mode is timed and leaderboard-ranked, and keeping it hint-free is what keeps that leaderboard fair.
Every ad request is non-personalized only: no advertising ID, no cross-app tracking, no App Tracking Transparency prompt, because there's nothing here to track you with. As part of delivering ads, AdMob's own SDK does incidentally collect some data on Google's infrastructure — device and coarse-location signals, and performance/crash diagnostics — independent of anything Kyu Sudoku itself reads, stores, or sends.
Notifications
If you turn on daily reminders in Settings, Kyu Sudoku asks your device for permission to send local notifications — the same kind of system prompt any app uses to ask before it can notify you. These reminders are scheduled entirely on your device using its own clock; nothing about whether you've turned them on, when they're scheduled, or whether you open one is ever sent to a server.
You can turn reminders off at any time in Settings, or deny or revoke the notification permission at the OS level — either way, nothing else about the app changes.
Keeping & deleting data
Server-side data is kept tied to your device ID for as long as you use the app. Since there's no login, we can't look you up by name or email — but if you want your leaderboard data deleted, email us your device ID (Settings shows a shortened version) and we'll remove it. Uninstalling the app deletes everything stored locally, including that device ID itself; a fresh install starts as a new, unlinked identity.
Children
Kyu Sudoku is a general-audience app, not directed at children under 13, and we don't knowingly collect data from them beyond what's described above.
Security
All traffic to our backend runs over HTTPS. The database key embedded in the app is scoped to a narrow set of server-side functions built for this purpose — it can't be used to read or modify anything outside the leaderboard tables.
Changes to this policy
If this policy changes in a way that affects what we collect or how it's used, the "Effective" date at the top will update. Meaningful changes will also be noted in the app's release notes.
Contact
Kyu Sudoku is built and run by an independent developer. Questions, deletion requests, or anything else — reach out at contact@nathanle.info.