Effective 13 October 2026
Who is responsible
Serhii Omelchenko is the developer and data controller for Blunderbook. For privacy questions or requests, email somelchenko.work@gmail.com.
Chess.com and Lichess
When you add a player, the app asks Chess.com or Lichess for that username's public profile and games, directly from your device. The username is part of the request, and, like any website, the site receives your connection's IP address and a header naming the app and its version. The app only reads public data: you never sign in, and it never asks for a password.
We do not receive these requests or their results. Chess.com and Lichess handle them under their own policies: see the Chess.com privacy policy and the Lichess privacy policy.
Your games and reviews
Tracked players, downloaded games, analyses and settings are stored locally on your iPhone. Stockfish runs on the device, so positions are never sent anywhere to be analysed. The app also keeps a small performance log on the device that records analysis timings and device conditions. It holds no usernames or games and is not sent anywhere. We do not receive a copy of any of this.
A backup you export contains your player names and games. It is your file, stored or shared wherever you choose. Removing the app removes its local data, unless the operating system preserves it in a device backup.
Anonymous usage events
To see how the app is used, it sends anonymous usage events to PostHog through its European service. This is on by default, and you can turn it off at any time under About, Privacy, “Share anonymous usage data”. Turning it off deletes any events not yet sent. If you turn it on again, the app starts with a new identifier.
The events cover opening and leaving the app, which screens you open, which site a player was added from, when you ask for an analysis and when one starts and ends (finished, failed or interrupted, with its depth, duration and number of moves), the outcome of a purchase attempt, and the kind of error when a download fails. Each event also carries the device model, iOS version, and app version and build.
Events are tied to a random identifier created on your device and replaced with a new one every year. It is not linked to you, your Apple Account, your device or your chess accounts. Usernames, games, positions and error messages are never sent. PostHog receives your connection's IP address to deliver the request, as any server does, and the app tells PostHog not to look up a location from it. No profile is built for the identifier, and the events are not used for advertising or shared with data brokers.
We rely on our legitimate interest in understanding and improving the app. You can object at any time by turning the setting off.
Purchases
Apple processes the Premium subscription. The app receives the transaction status and product identifier needed to grant or restore Premium on your device. This processing is necessary to perform the purchase contract and to prevent fraud. We do not receive your payment-card details or your Apple Account. See Apple’s privacy policy.
Support
If you email us, we receive your email address and the information you choose to include. We use it to answer your request or investigate a problem. This is based on taking steps at your request and our legitimate interest in supporting the app. Correspondence is normally deleted within 24 months after the matter is closed, unless it must be kept longer to establish or defend a legal claim.
Retention
Games, reviews and settings remain on your device until you delete them in the app, remove the app, or the operating system removes them. Usage events are kept for as long as they help us understand how the app is used, and for no more than 24 months. Apple retains purchase records, and Chess.com and Lichess retain request data, under their own policies.
International transfers
Usage events go to PostHog's service in the European Union. Apple, Chess.com, Lichess and their service providers may process information outside the European Economic Area. Their privacy notices explain the locations and safeguards they use for these transfers.
Sharing and sale
We do not sell your data or use it for advertising. The app contains no ads and no tracking. Information handled by Apple, Chess.com or Lichess is governed by their policies.
Your rights
Depending on the processing, you may ask to access, correct, delete, restrict or receive your personal data, or object to its use. You can stop usage events at any time from the app's About screen.
The developer does not receive your locally stored games or reviews. You can remove them in the app or by deleting the app. Because usage events are tied only to a random identifier, we cannot usually match them to you. Requests about data held by Apple, Chess.com or Lichess should be made through their own privacy tools. To exercise rights concerning information held by the developer, use the email address below. You may also complain to the Dutch Data Protection Authority or the authority where you live or work.
Automated decisions
We do not use personal data to make automated decisions that produce legal or similarly significant effects about you.
Contact
For privacy questions or support, email somelchenko.work@gmail.com.
Changes
We may update this policy when the app, its providers, or legal requirements change. The effective date above identifies the current version.