Can I sync Shellf between iPhone and Android?

Shellf accounts are device-agnostic. Your library, ratings, and taste profile aren’t stored on the device — they live on Shellf’s server (Supabase / PostgreSQL, hosted in the EU). The mobile app is a thin client over that server. Sign in on a different device with the same email, and everything you’ve built shows up.

Right now Shellf is Android-only on mobile. The website at shellf.app has some basic features such as authentication, library import, library export, and account management.

When iOS launches May 2026, installing the iOS app and signing in with your existing Shellf account is all it takes — your library, ratings, taste profile, and shelves appear automatically. Same the other way: if you start on iOS and pick up an Android later, you don’t lose anything. There’s no differences between platform.

Sync is on-demand, not real-time. When you make a change on one device (rate a book, add to a shelf, mark DNF), it’s written to Shellf’s server immediately. When the second device next opens or pulls to refresh, it sees the change. There isn’t a websocket pushing updates — this is good enough for a tracker (you’re not collaborating in real time on the same library) and avoids the battery cost of a persistent connection.

Conflict resolution: last write wins. If you somehow rate the same book a 3 on Android and a 4 on iPhone within the same minute, the most recent write is the one that sticks. In practice, this almost never matters — nobody’s racing themselves to rate a book.

The mobile app caches your library locally so you can browse and even rate books without a connection — the cached changes sync up next time you’re online. AI recommendations and book search require a network round-trip and won’t work offline. This is by design: the recommendation engine is server-side and the catalogue is too large to push to the device.