Sync engines, conflict resolution, and the data patterns we use to build apps that work even when the network doesn't.
Offline-first isn't a feature you sprinkle on a connected app. It's a discipline that shapes your data model, your UI, and your team's mental model of how the app works. Retrofitting it onto a server-of-truth architecture is almost always more expensive than rewriting the data layer from scratch.
The conflict resolution problem
Every offline-first system eventually faces the same question: two devices edited the same record while disconnected — what wins? The answer determines your architecture. "Last write wins" is simple and frequently wrong. CRDTs are correct and frequently overkill. Operational transforms are powerful and frequently overengineered. Pick deliberately, because changing later is brutal.
Sync engines worth using
The 2026 mobile sync landscape is healthier than it's ever been. Replicache, ElectricSQL, PowerSync, and Triplit all solve real problems with mature SDKs. The choice depends mostly on your backend constraints and how much custom conflict logic you need. For greenfield apps, we lean toward ElectricSQL or PowerSync when the backend is Postgres-native, Replicache when the team wants tight control over the sync protocol.
- Local data is the source of truth — the server is the eventual reconciler
- Every write is optimistic, with explicit conflict resolution rules
- Use schema migrations on both client and server with explicit version gates
- Build a sync status UI from day one — users need to trust the model
“In an offline-first app, the local database is the source of truth. The server is just the place where truths meet.”
UX patterns that earn trust
The UX challenge isn't the offline state — it's the moment of reconnection. Users need to know what synced, what didn't, and what's about to change under them. Show pending writes explicitly. Surface conflicts before they resolve silently. Treat the sync status as a first-class UI surface, not a hidden affordance buried in settings.
Start with the sync model. The data layer is the foundation everything else rests on, and the apps that fail at offline-first almost always fail because they decided the data model after the screens.
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