Stacks Privacy Policy

Last updated: July 27, 2026

Stacks is a book-tracking app that lets you keep track of what you're reading and see what your friends are reading. This policy explains what information Stacks collects, how it is used, and the choices you have. If you have any questions, contact us at kpully@gmail.com.

Information we collect

• Phone number. You sign in with your phone number, which we use to authenticate your account and as your unique identifier so friends can find you.
• Profile details. Your display name and, optionally, a profile photo you choose or take.
• Reading activity. The books you add to your stacks, their status (want to read, reading, read), and any ratings you give them.
• Friends. The connections you make with other Stacks users.
• Contacts (only when you use Find Friends). If you choose to look for friends, Stacks reads the phone numbers in your device contacts to check which of them already have a Stacks account, and to let you know later if one of them joins. See below for how these are handled.
• Crash and diagnostic data. When the app crashes or hits an error, Stacks collects diagnostic information — such as your device model, operating system version, and the technical details of the crash — through Google Firebase Crashlytics. This helps us find and fix problems. It is not used to identify you or to track you across other apps.

How we use your contacts

When you tap Find Friends and grant contacts permission, the phone numbers from your contacts are sent to our server solely to match them against existing Stacks users. Phone numbers that match an existing user are not stored — they are used only for that lookup. Connecting with a match is always something you choose; it is never automatic just because a number is in your contacts.

For numbers that don't match anyone yet, we keep a one-way cryptographic hash of the number — not the number itself — so that if that person joins Stacks later, we can let you know. A hash cannot be turned back into a phone number. It's deleted as soon as that person joins and you've been notified. Stacks does not use your contacts for advertising and never sells them.

How your information is shared

• With your friends. Your display name, profile photo, and reading activity are visible to people you are connected with on Stacks (this is what appears in their feed).
• With service providers. Stacks uses Google Firebase (authentication, database, file storage, cloud functions, and crash reporting) to operate the app, and the Open Library service to look up book details and cover images. Your data is processed by Firebase on our behalf.
• No advertising or cross-app tracking. Stacks does not include third-party advertising and does not track you across other companies' apps or websites. The only diagnostic tool we use is Firebase Crashlytics (described above), solely to monitor and fix crashes.

Data retention and deletion

We keep your information for as long as your account is active. You can permanently delete your account at any time from the Profile screen (Delete Account). Deleting your account removes your profile, reading activity, friend connections, uploaded photo, and your authentication record. This action cannot be undone.

Security

Your data is stored using Google Firebase and protected by access rules that restrict it to you and, where applicable, your friends. No method of transmission or storage is completely secure, but we take reasonable measures to protect your information.

Children

Stacks is not directed to children under 13, and we do not knowingly collect personal information from them. If you believe a child has provided us information, contact us and we will delete it.

Changes to this policy

We may update this policy from time to time. When we do, we will revise the "Last updated" date above. Continued use of Stacks after a change means you accept the updated policy.

Contact

Questions or requests about your data? Email kpully@gmail.com.