Privacy policy

Last updated 20 October 2026

Letterlight is a journal app for Android. This page explains what happens to what you write.

What stays on your phone

• Your journal entries, moods, letters, replies, routine and practices are saved only in the app's storage on your device.
• Files you attach as sources (PDFs, images, text) are copied into the app's storage on your device.
• Your Anthropic API key, if you enter one, is saved on your device.
• There is no Letterlight account and no Letterlight server. We never receive your journal.

What is sent to Anthropic

Letters are written by Claude, an AI model made by Anthropic. When you ask for a letter, a reply or a translation, the app sends these to Anthropic's API:

• the entry and mood you're asking about, and the earlier letters and replies in that conversation;
• any sources attached to that entry;
• the mentor you chose, your app language and the local date and time;
• for routine and practice reminders, the habit or exercise they are about.

Anthropic processes this under its own terms and privacy policy. If you use your own API key, the requests go to Anthropic under your own account.

Web pages you add

When you add a web page as a source, the app downloads that page directly from its website once and keeps its text on your device.

What we don't do

• No analytics, advertising or tracking libraries.
• No selling or sharing of your data.
• Notifications are scheduled on your phone; no push server is involved.

Deleting your data

Delete entries in the app, or uninstall Letterlight to remove everything it stored on your device. Clearing the app's storage in Android settings does the same.

Children

Letterlight is not directed at children under 13.

Contact

Questions about this policy: hello@letterlight.app