Effective date: 2026-10-02

This Privacy Policy explains how StackBooks ("we," "us," or "our") collects, uses, and shares information when you use the StackBooks mobile application (the "App"). By using the App, you agree to this Policy.

1. Information We Collect

1.1 Information You Provide

As you use the App, information is created and stored on your device, such as:

• books you register (title, author, publisher, ISBN, page count, reading status, finished date);
• ratings, tags, and notes you write about each book;
• cover images you take with the camera or choose from your photo library;
• app settings (such as stack units, language, and display preferences).

This information is stored locally on your device, in the App's own storage area. The App does not require an account, and we do not operate our own servers to store your books, notes, or cover images. Your library is never sent to us.

If you use the in-app backup feature (Settings > Data > Export), your data is written to a file that stays under your control (for example, saved or shared through your device). This backup file includes everything you entered, such as notes and cover images. We do not receive or store exported files; once you share or move a file, keeping it secure is your responsibility.

1.2 Book Search

When you search for a book by title, author, or ISBN, scan a barcode, or browse book lists in the App (such as popular books), the App sends the search term or ISBN, together with standard request information such as your IP address, to servers we use and to external bibliographic data services, so that we can retrieve bibliographic information and cover images.

We send only what is needed to look up a book. Your notes, ratings, tags, and reading status are never sent. We do not use your search terms for advertising or profiling, and we have no way to connect them to your books, notes, or any account — the App does not have accounts.

To avoid looking up the same book repeatedly, search results — together with the search terms or ISBNs used to look them up — may be stored temporarily on the servers we use. They are kept for a limited period and then deleted automatically. They are not linked to you, your device, or your library.

1.3 Analytics and Crash Reporting

The App uses the following Google services (Firebase) to understand how the App is used and to keep it stable:

Firebase Analytics (Google):

• anonymous usage events only (for example: app launch, registering a book, scanning a barcode, and opening a bookstore link);
• device and app information (such as device model, OS version, app version, language/region, and an app instance identifier).