Privacy Policy

Last updated: 10 September 2026

Your games, moves, positions and engine analysis are not uploaded automatically. All chess analysis (Stockfish, Maia-2) runs entirely on-device. BlunderZero sends limited product analytics and crash diagnostics, described below, but not the contents of your chess games. Cloud Backup is a button you press, and this policy explains exactly what it sends, where it goes, and how to delete it.

Data we collect automatically

Limited app usage analytics and crash diagnostics, via Google Firebase (Analytics and Crashlytics). Examples: which screens are used, that a drill was completed, that the app crashed and the technical stack trace of the crash. Event values are categorical labels and bucketed counts, never chess game content.
This data is tied to a randomly generated app identifier. It does not contain your name or email address. Because that identifier is stable, the data is pseudonymous rather than anonymous.
We do not send your Lichess or Chess.com username to Analytics. An earlier version of the app did, as an Analytics user property. We stopped in July 2026, and in September 2026 we deleted those historical records from our warehouse.
That identifier comes from an anonymous Firebase account the app creates automatically on first launch. It is not a sign-up, asks nothing of you, and holds no personal details, but it is what links your usage analytics and crash reports to each other over time. There is currently no in-app setting to turn this off.
Google's analytics service derives coarse location (country or region, from IP address), device model, and OS version. The IP address itself is not stored in our analytics exports.
BlunderZero shows you no ads. We do link Google Analytics to a Google Ads account, so limited analytics data may be used to measure and improve how we promote BlunderZero, including which advertising reaches people who go on to use the app. We do not sell this data.

Chess data stored on your device

Games you play or import, their analysis, your drills and practice history, your opening choices, and your progress. All of it lives in the app's sandboxed database on your phone.
Player progression (level, XP, achievements, streak), stored in device preferences.
Coach detector telemetry powering the in-app "Coach detector insights" view. Local only; clear it any time via that screen's "Clear telemetry" button.

None of this leaves your device unless you use Cloud Backup.

Cloud backup

Cloud Backup is optional and manual. Nothing is uploaded unless you open Settings, go to Backup & Restore, and press Backup. There is no automatic, scheduled or background upload.

When you do press it, your backup is stored in Google Firestore, in a project we operate, under the anonymous identifier described above. It is transmitted over an encrypted connection. We do not sell your backup or disclose it to third parties for their own purposes. Google Firebase stores and processes it for us as our service provider.

What a backup contains

Every game you have played or imported, in full, including the moves and positions.
The engine's analysis of those games.
Your drills, your practice attempts and your progress on them.
Coaching history: what the app diagnosed, what it suggested, and what you did next.
A derived picture of your chess strengths and weaknesses.
Your saved opening moves and study schedule, and your warm-up puzzle history.
Any notes you typed yourself during a game. These are free text, up to 120 characters each. We do not review or moderate the content of these notes, so please do not type anything there you would not want stored.

Games you import from Lichess or Chess.com include your opponent's public username and the public game identifier from that site, so a backup is not exclusively your own data.

Third-party sources you may connect to

Lichess and Chess.com game archives. Connections happen directly from your device to those services. Your platform username is used on-device to fetch and label your games, and the current app does not attach it to our analytics. See the note above about earlier versions.

Data retention

Usage analytics in Google Analytics are retained for 14 months and then deleted automatically.
Crash diagnostics are retained for 90 days (Firebase Crashlytics' standard retention).
Analytics exported to our BigQuery warehouse are retained for about 14 months.
Cloud backups are kept until you delete them. They do not expire on a timer, because the point of a backup is that it is still there when you need it. You control removal, as described below.

Deleting your data

Deleting your cloud backup

Settings, then Backup & Restore, then Delete cloud backup. This permanently removes everything backed up from the app: your games, analysis, drills, practice history and notes. Your data on the device is not affected.

If the deletion does not fully complete, the app tells you so and you can press it again. It is safe to repeat.

Deleting a single game

Deleting a game in the app removes it and its analysis, drills, coaching history and notes from your device immediately.

Its copy in your cloud backup is removed on your next successful backup, not at the moment you delete it. Until then, the app remembers the deletion and will not restore that game onto this installation. If you delete a game, never back up again, and then uninstall or clear the app's data, that record of the deletion is lost while the older cloud backup remains. Delete cloud backup is the action that covers that case, and it works whether or not you have backed up since.

Uninstalling

Uninstalling deletes all locally stored data and stops all collection. It does not delete a cloud backup you have already made. Use Delete cloud backup first if you want it gone.

Analytics and crash data

Already-collected pseudonymous analytics and crash records are deleted automatically at the end of the retention periods above. You may email us to request earlier deletion. Because the analytics identifier is random and not shown in the app today, we may be unable to isolate your specific installation's records from your description alone; records we cannot isolate still expire on the retention schedule above.

Children

The app is not directed at users under 13.

Changes

If this policy changes, the new version will be linked from the app and the store listing.

Contact

support@socialplayai.com