How I Built an Offline-First Sync Engine for Flutter Apps

Developing mobile apps that work reliably offline is much harder than it sounds.

Most apps today assume the network is always available. But in reality, users often experience:

• slow connections
• unstable networks
• complete offline situations

When this happens, apps usually break.

While working on several Flutter projects, I realized that building offline-first architecture repeatedly requires implementing a lot of complex infrastructure:

• queueing operations locally
• retry logic for failed requests
• conflict resolution between devices
• background synchronization
• delta updates to avoid sending full documents
• handling network reconnections

Every project required rebuilding the same logic again and again.

So I decided to build a package that handles all of this automatically.

I called it SyncLayer.

---

The Idea

The goal of SyncLayer is simple:

Save data locally first, then synchronize it automatically in the background.

This means the app always feels fast and responsive, even when the device is offline.

Example usage looks like this:

dart
await SyncLayer.init(
  SyncConfig(
    baseUrl: 'https://api.example.com',
    collections: ['todos'],
  ),
);

await SyncLayer.collection('todos').save({
  'text': 'Buy groceries',
  'done': false,
});