Privacy policy

Updated: 20 October 2026

LeziBook reads aloud books that you put on your own phone. It is built on one rule: your books’ content stays on your phone. This policy says what the app and our servers process, why, for how long, and how you control it.

Some features below (accounts and sync, the paid plan, AI text clean-up) are not in the current version. We describe them now so you know what will change when they arrive. Each runs only when you turn it on.

1. Who is responsible

Controller: Lê Bá Trọng, an individual developer publishing as USelf Labs (“USelf Labs”, “we”), Ho Chi Minh City, Vietnam. Privacy contact: support@uselflabs.com.

2. What stays on your phone only

The following is created and processed entirely on your phone and never sent to us or anyone:

• The book files you import (EPUB, PDF, TXT, DOCX), their text, covers and contents.
• The text prepared for reading aloud, and the voice audio made from your books.
• Your library, reading and listening positions, bookmarks and display settings.
• Your reading and listening statistics (minutes, streaks, books finished).

Deleting a book deletes its data and cache on the phone. Uninstalling the app deletes all of it.

The app has no DRM-removal feature and refuses DRM-protected files.

3. What we receive and why

3.1 Anonymous usage statistics

To know whether the app works and to fix problems, the app sends anonymous events such as: app opened, import succeeded or failed (format, size, chapter count), listening started and stopped (voice type, speed, duration), voice downloaded, on-device voice speed, display setting changed.

• Each batch carries a random install ID made on the phone, the app version, the operating system and a device-class code. The ID is not linked to your name, email, phone number or account.
• Events never contain book content, titles, authors, file names or any text.
• Events are never joined with an account (if you have one later).
• Kept for up to 90 days, then deleted automatically.
• Sent only if you agree. The first time you open the app, it asks whether you agree to send usage data and error reports. Until you answer, or if you choose No, the app records and sends nothing.
• You can change your choice at any time in Settings › Privacy › “Send usage data and error reports”. When off, the app stops recording and deletes unsent events.

Legal basis: your consent, which you can withdraw at any time with that switch.

3.2 Crash reports

When the app or server fails, we receive the error type, its location in the code and the version. Reports are filtered so they do not contain error messages, request contents, titles or text. They are kept on a system we run ourselves for up to 30 days. The switch in 3.1 also turns crash reports off.

3.3 Configuration, dictionaries and voices

The app periodically downloads configuration, the abbreviation dictionary and the voice catalog, and downloads the voice files you choose. These requests carry no personal data beyond the IP address every internet connection has (see 3.6).

3.4 Launch waitlist (on lezibook.uselflabs.com)

If you leave your email to hear about the launch, we store your email, platform (Android or iPhone) and the page language. Nothing else.

• Its only purpose: sending one email when the app is in the stores.
• The whole list is deleted after that email, including from backups within the backup retention period.
• No marketing emails, no sharing with third parties.
• To be removed earlier, email support@uselflabs.com.

Legal basis: your consent when submitting the form.

3.5 When you contact us

If you email support (our mailbox runs on Lark), we use your address and message to answer you and keep them as long as needed to handle the request, at most 12 months.

3.6 IP addresses and technical logs

Every connection to our servers passes through Cloudflare (section 5), which processes IP addresses to route traffic and stop attacks. Our server keeps no access log, does not log IP addresses and never logs request contents.

4. Coming features (only if you turn them on)

4.1 Accounts and sync

The app is fully usable without an account. If you later sign in with Apple or Google to use several devices:

• Signing in turns sync on. The server keeps, for your account: the account identifier issued by Apple or Google, and library data: a hash of each file, title, author, genre, language, format, chapter count, progress, reading and listening positions, bookmarks, settings and reading statistics.
• Never synced: book files, text, covers or audio. On a new device, books show as “not on this device” until you import the file again.
• This data is encrypted in transit and at rest and serves only you: not used for aggregate analytics, recommendations based on other people, model training or advertising, and never sold or shared.
• “Delete synced data” (keeps the account) and “Delete account” are in the app. Data is removed from the server within 30 days, including from backups within the backup retention period.

Legal basis: your consent when signing in, and performing the sync service you request.

4.2 Paid plan

Payment is handled by the Apple App Store or Google Play; we never receive card or payment details. The server receives the store receipt to confirm your plan and keeps the plan status and AI quota usage for your account.

4.3 AI text clean-up

This is the only case where book text leaves the phone, and only when you turn it on for a particular book:

• The app sends passages (up to 4,000 characters each) through our server to Google Gemini (paid API tier) to fix formatting and write numbers and abbreviations out as words.
• Our server processes them in memory only: it does not store or log the passages or the results. The results are stored only on your phone.
• Under Google’s paid API terms, data sent through the API is not used to train models. Google acts as a processor for this feature.
• Passages are sent without the book title, file name or account information.

5. Processors

We do not sell personal data. We use only these infrastructure providers, each for its own task:

Our server is located in Vietnam; voice files and encrypted backups are stored on Cloudflare R2. Cloudflare, Google, Apple and Lark may process data in other countries; we complete the cross-border transfer formalities that apply. The launch email is sent once from our own support@uselflabs.com mailbox on Lark, not through a bulk mailing service.

6. Retention

7. Your rights

Under Vietnamese personal data protection law you may be informed, give or withdraw consent, access, correct, delete, restrict or object to processing, and complain. How:

• Turn off statistics and crash reports: Settings › Privacy.
• Delete data on the phone: delete books in the app, Settings › Storage on this device, or uninstall.
• Delete synced data or your account (when available): in the app.
• Anything else, including leaving the waitlist: support@uselflabs.com. We answer within 30 days.

Because the anonymous statistics are not linked to your identity, we cannot find which events are yours; the switch is how you stop them.

8. Security

Connections to our server use HTTPS. The AI service key lives only on the server. Pre-generated audio is encrypted with a key kept in the phone’s Keychain or Keystore. Account data (when available) is encrypted at rest. Off-site backups are encrypted. No system is perfectly secure; if an incident affects personal data, we will notify as the law requires.

9. Children

LeziBook is not aimed at children under 16. If you are a parent and believe your child joined the waitlist or created an account, contact us and we will delete it.

10. Changes

When this policy changes we update the date at the top. Important changes (for example when accounts, the paid plan or AI text clean-up launch) are announced in the app before they take effect.

11. Contact

support@uselflabs.com · Lê Bá Trọng (USelf Labs), Ho Chi Minh City, Vietnam