NER Cycle App (Arbeitstitel)

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A local-first, open-source mobile app (Android + iOS, PWA bonus) for tracking menstrual-cycle symptoms and manually evaluating them per NER rules (Rötzer), in the INER spirit — the user places the marks and stays the authority; the app is a tool (visualization, arithmetic, statistics), not the decision-maker.

The app supports, it never decides. The product shape is "Mode M" (NFP/NER assisted marking, see ADR-0001, status: Accepted — by owner decision, 2026-09-19). The user/couple stays in control and takes conscious decisions; the app computes and warns about arithmetic, but never gives a fertility verdict. Knowing the method (book or course) is a prerequisite for reliable interpretation. This posture is the owner's, not endorsed by INER. For the full picture read docs/product/vision.md.

This app is in beta. A beta can still lose data, so export your data regularly and before every update — via the JSON export in the settings screen. Everything is stored locally on your device, and the JSON export is the one backup path on all platforms (see Backup, migration & recovery).

• Package name cycle_app is an explicit PLACEHOLDER (ADR-0002) — rename is a one-line pubspec.yaml change later.
• ⚠️ license — chosen, final confirmation open: the license has been chosen (2026-09): Apache-2.0 — full text in the LICENSE file at the repo root. The tree is distributed under Apache-2.0; the final confirmation before the first published release is still open.
• Local-first: no cloud, no analytics; data stays on the device (drift/SQLite, encrypted on native platforms later — ADR-0005).

Installation

Install the app on an Android device — no Flutter SDK, no development setup needed. (An iOS build does not exist yet.)

What to expect: the app supports observing and computing/visualizing only — it does not interpret your data, advise, or give a fertility verdict. Knowing the method (book or course) is a prerequisite for reliable interpretation; see the "The app supports, it never decides" block above for the full posture.

Where to get it

Download an APK from the GitHub releases page. Each release carries three release-signed APKs — one per device architecture (ABI), named cycle-app-<version>-<abi>.apk where <version> is the release's version number, e.g. cycle-app-0.2.0-arm64-v8a.apk. Pick the one matching your phone:

• cycle-app-<version>-arm64-v8a.apk — modern phones (the right choice for most devices),
• cycle-app-<version>-armeabi-v7a.apk — older 32-bit devices,
• cycle-app-<version>-x86_64.apk — mainly emulators.

Not sure which? Check Settings → About phone for the processor information, or — with the phone connected to a computer and developer options enabled — run adb shell getprop ro.product.cpu.abi. All three APKs are signed with the same release key. Every release note lists each APK's SHA-256 checksum plus the signing certificate's SHA-256 fingerprint, so you can verify the download if you want to.

Not ready to install? Try the web demo

There is also a public web demo at BenediktBurger.github.io/cycle-app: the app running in your browser, nothing to install. Mind that entries made there stay in that browser (no sync, no upload) — the browser storage is not encrypted, and as a beta the demo can still lose data, so only enter data you are comfortable losing or exposing. The demo page spells out what that means.

Installing

1. Download the APK matching your device (see above) from the latest release.
2. Open the downloaded file on the device.
3. Android will warn about installing apps from an external source (sideloading / "unknown sources") — accept it to continue.
4. Expect an additional "unknown developer" / "unsafe app" style Play-Protect remark: the app is signed with the project's own key and is not distributed through a store. This is expected, not a sign that something is wrong with the file.

Updating

Download the most recent APK for your device's architecture (the same one you installed before) from the releases page and install it over the existing version. Because the signing certificate stays the same, Android updates the app in place instead of treating it as a new install, and your data stays. That said: this is a beta — data loss is not ruled out, so exporting your data (JSON export in the settings screen) before updating is necessary, and exporting regularly while you use the app is wise.

Privacy note

The app is fully offline: no network access, no analytics. All data stays on your device.

Found an issue or have a suggestion? Please open an issue at github.com/BenediktBurger/cycle-app/issues — feedback is very welcome.

Installation (Deutsch)

Deutsche Fassung des Wichtigsten für deutschsprachige Nutzer — Installationsweg, Beta- und Backup-Hinweis, Charakter der App, Feedback:

Die App unterstützt die Beobachtung des Zyklus: Sie erfassen jeden Tag Ihre Daten, und die App rechnet und zeigt an — sie schlägt nichts vor und entscheidet nichts. Methodenkenntnisse (aus einem Lehrbuch oder einer Schulung) sind Voraussetzung für eine zuverlässige Beurteilung.

Beta-Hinweis: Die App befindet sich in der Beta-Phase. Datenverlust ist nicht ausgeschlossen — exportieren Sie Ihre Daten deshalb regelmäßig und vor jedem Update über den JSON-Export in den Einstellungen. Alle Daten liegen lokal auf dem Gerät; der JSON-Export ist auf allen Plattformen der einzige Backup-Weg (Einzelheiten: Backup, migration & recovery (auf Englisch)).

Installation (Android): Eine iOS-Version gibt es noch nicht.

1. Laden Sie die zu Ihrem Gerät passende APK von der GitHub-Releases-Seite herunter. Jedes Release enthält drei APKs — eine pro Gerätearchitektur:

   • cycle-app-<version>-arm64-v8a.apk — moderne Telefone (die richtige Wahl für die meisten Geräte),
   • cycle-app-<version>-armeabi-v7a.apk — ältere 32-Bit-Geräte,
   • cycle-app-<version>-x86_64.apk — hauptsächlich Emulatoren.

2. Öffnen Sie die heruntergeladene Datei auf dem Gerät und bestätigen Sie die Warnung zum Installieren aus einer externen Quelle (Sideload / „unbekannte Quellen“).

3. Ein zusätzlicher Play-Protect-Hinweis („unbekannter Entwickler“) ist zu erwarten: Die App ist mit dem eigenen Schlüssel des Projekts signiert und wird über keinen Store verteilt — das ist normal und kein Zeichen für ein Problem.

Aktualisierung

Laden Sie die neueste APK für dieselbe Architektur herunter und installieren Sie sie über die bestehende Version. Da der Signaturschlüssel gleich bleibt, wird die App an Ort und Stelle aktualisiert und Ihre Daten bleiben erhalten — aber: exportieren Sie vorher (siehe Beta-Hinweis oben).

Fehler gefunden oder Verbesserungsvorschlag? Bitte öffnen Sie ein Issue auf GitHub.

Getting started

flutter pub get
flutter run -d chrome

Requires a Flutter stable SDK (any location with <sdk>/bin on PATH). See CONTRIBUTING.md for the full setup, platform scaffolding, and the analyze/test/build commands — notably flutter pub get before flutter test.

Tech stack

• Flutter stable (web as iteration target, per ADR-0003; product targets Android + iOS)
• flutter_riverpod for state management (ADR-0004)
• drift / SQLite for local-first storage (ADR-0005)
• flutter gen-l10n for localization, German-first with English mirrored

Project layout / docs

• docs/product/vision.md — product vision and requirements.
• docs/adr/README.md — architecture decision records (ADR-0001 … ADR-0007 — 0007 is the language policy).
• docs/dev-notes.md — operational lessons and how-tos.
• docs/roadmap.md — open work / upcoming milestones (to-do list; history lives in git).
• .github/workflows/ci.yml — GitHub Actions CI: flutter analyze, flutter test, flutter build web (ADR-0006).

Status

Working app: Tagebuch / Zyklus / Statistik / Einstellungen on a local drift database (SQLite file on Android/iOS, WebAssembly/OPFS in the browser; data persists across reloads), with JSON export/import. The UI is German-first with an English switch, including the Mode-M marking UI (first higher measurement, mucus peak, SUZ — computed evaluation marks on the cycle chart, see docs/roadmap.md for open work).

Screenshots

Two screenshots of the current app (cycle chart and diary) are in the fastlane store metadata: 01 and 02 (shown in English, matching the en-US store listing).

Backup, migration & recovery

Backup, data migration to another device, and data recovery all happen through the JSON export/import in the Einstellungen (settings) pane — and nowhere else:

• Export regularly to a file you control (Einstellungen › JSON-Export) and import it on the target device to restore/re-migrate your data there.
• Never copy the database file itself (Android/iOS): there the database is encrypted with a device-bound key (see ADR-0005), so a copied file is unopenable data on anything else — not a backup.
• On the web build the browser storage (OPFS/IndexedDB) is not encrypted by the app (web stays an unencrypted development tool) — the public web demo states what that means for demo users.

JSON export/import is the only backup path on all platforms — web included.

Import from drip

The Einstellungen screen can import a CSV export of the drip cycle tracker (a sibling project): paste it anywhere (a file picker is offered on the web). Rows merge into the main profile with the same overwrite-by-date policy as the JSON import, so re-importing the same export adds no duplicates. Per day, drip's bleeding, temperature, mucus (including the S+ → slippery egg-white decode), desire, sex, pain, mood, cervix words, and notes are mapped into the NFP diary. Lost in the import: the per-symptom exclude flags other than the temperature one (an excluded temperature just marks the day) and the temperature measurement time.

Five mapping decisions below are awaiting NFP expert (INER) review — they are also marked TODO(user-review) in the code:

• Light/medium/heavy bleeding all collapse into a single "period" entry.
• Drip's "temperature excluded" becomes a generic interrupted day; the reason for the exclusion is not stored.
• The mucus decode works on drip's combined NFP number, so texture nuances are lost: any NFP 4 — including one drip derived from a slippery feeling — imports as S with egg-white quality (≙ S+), whereas a slippery feeling recorded without a texture imports no mucus at all (mirrors drip; the creamy nuance is likewise lost).
• Cervix observations become free-text English words, and out-of-range indices are clamped to the nearest valid one.
• Symptom notes concatenate after the day note as [temp]/[pain]/[sex]/[mood] prefixed lines.

License

Apache-2.0 — chosen (owner decision, 2026-09); the full text is in the LICENSE file at the repo root. The final confirmation before the first published release is still open.

One shipped asset already carries its own license: the bundled Noto Sans Regular font (used by the PDF export so note text renders beyond Latin-1) is Google's, licensed under the SIL Open Font License 1.1 — see assets/fonts/LICENSE-NotoSans.txt.