Luteal

A menstrual cycle tracker for Android, built around one rule: what you recorded and what the app calculated are never presented as the same thing.

Recorded observations are labelled as recorded. Predictions are labelled as estimates, shown as a range rather than a confident date, and the app says what the range was derived from. Luteal makes no diagnosis.

The app is French-first; English is also shipped. It works entirely offline by default, with optional end-to-end encrypted sync.

Privacy

• Tracking data lives in a local Room database. Nothing leaves the device until sync is explicitly enabled - SyncMode defaults to OFFLINE_LOCAL.
• Android cloud backup is disabled for the app's data (allowBackup=false).
• Home-screen widgets start concealed and never show private notes or detailed observations. Revealing a widget sends its visible content to the launcher, which may retain previews or screenshots outside Luteal's control.
• No advertising, no analytics, no Google Play Services, no Firebase.
• Crash reporting is ACRA with a consent dialog: nothing is sent unless the user reads it and chooses to send. Tracking data is not included.
• When sync is on, records are encrypted on-device before upload; the server stores only ciphertext. See docs/architecture/E2EE_DESIGN.md.

Building

Requires JDK 21 and the Android SDK (compileSdk 37, minSdk 26).

./gradlew assembleDebug          # debug build
./gradlew testDebugUnitTest      # unit tests
./gradlew assembleRelease        # release build

A plain clone builds with no other checkout present: the folicular API contract is vendored under contract/.

Release signing reads keystore.properties at the repository root - copy keystore.properties.example and fill it in. Without that file the release build is left unsigned rather than falling back to the debug key.

Layout

Path	Contents
app/src/main/java/fr/luteal/app	Screens, navigation, view models, DI wiring
app/src/main/java/fr/luteal/core	Domain model, Room storage, sync, crypto
contract/	Vendored folicular OpenAPI spec and conformance fixtures
docs/architecture	Sync boundary, E2EE design, backend integration
docs/product	Feature research, roadmap, and widget behavior
docs/research	Cycle research notes and source register
fastlane/	F-Droid listing metadata

Backend

Sync talks to folicular, a Go service. It is optional: the app is fully usable without it. The server address defaults to the official Luteal service (BuildConfig.SYNC_BASE_URL) and can be pointed to any self-hosted folicular instance in Settings.

Licence

GNU General Public License v3.0 or later. See LICENSE.

Luteal is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.