Scaleup Guide
Building Offline-First Mobile Apps: Sync Strategies That Work
In this guide
A simple guide to Building Offline-First Mobile Apps: Sync Strategies That Work. Learn what to build first, what to check, and where mistakes usually happen.
Connectivity is unreliable. The best mobile apps treat the network as an enhancement, not a requirement. An offline-first architecture stores data locally and syncs in the background.
The Core Principle: Local Is the Source of Truth
Read and write to a local database first (SQLite/Drift, Realm, WatermelonDB). The UI never waits for the network. A sync layer reconciles local changes with the server when a connection is available.
Optimistic Writes
- Apply the change locally and update the UI immediately.
- Queue the mutation for sync with a 'pending' flag.
- On reconnect, push queued mutations; on success, mark them synced.
- On conflict, resolve with a strategy (last-write-wins, or merge).
Conflict Resolution
The hard part of sync. Simple apps use last-write-wins with timestamps. Collaborative apps need CRDTs or server-authoritative merges. Decide early — retrofitting conflict handling is painful.
Don't Forget the Queue
Persist the mutation queue to disk. If the app is killed before sync, an in-memory queue loses the user's offline edits — the exact failure offline-first is meant to prevent.