I built a period tracker that never asks for an account
This week I shipped the first public version of Mori, an Android period tracker. The product rule I started with was simple: no account, ever, for the core features. Why that rule Period data is some of the most sensitive stuff on a phone. In most tracker apps it ends up on a company server, attached to an email, behind a login the app demands before it even opens. That model has real-world…
Mori is a new Android period tracker app that was recently released. The developer chose to design the app with a unique rule: no account requirements for core features. This decision was made because period data is highly sensitive information on a phone. In most tracker apps, this data is sent to a company server when users log in, which can lead to legal consequences if subpoenaed, especially after major rulings like Roe v.
Wade. The app stores records locally on the user's phone using a SQLite database, ensuring that no data leaves the device unless the user chooses to encrypt it and sync it to a cloud server. Unlike other apps, Mori does not require users to sign up for an account before using its basic features. Users can open the app, mark their period days on the calendar, and the app will provide predictions for their next period, along with an ovulation and fertile window estimate.
These predictions are based on the user's historical data and are presented as estimates, not medical certainty. The app also offers optional local notifications and the ability to export and delete all data on-device. The paid version of Mori, which costs $3.99 as a one-time purchase, offers optional encrypted cloud sync. The backend that handles this sync is built using Go and Postgres, and it encrypts the snapshot of data on the user's device before uploading it to the server.
The server can unwrap the encrypted data during account recovery, but this is transparently handled and the user is made aware of this process. The app is currently available as a side-loaded APK on the developer's website, and iOS support is planned but not started. The developer discussed various aspects of the app's design, including its sync crypto design, the deterministic prediction approach, and the choice of language for the landing page.
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