What is Offline-First Progressive Web App (PWA)?

Offline-First PWAs invert the traditional assumption that web applications require constant internet connectivity. Instead of treating offline as an error state, they treat it as the default state. The architecture uses three layers. The Storage Layer uses IndexedDB (or SQLite via WASM) to maintain a complete local database replica on the device. Every read and write operation hits the local database first, ensuring instant response times regardless of network conditions. The Sync Layer implements background synchronization using Service Workers that detect connectivity changes and queue mutations for upload. The Conflict Resolution Layer uses CRDTs (Conflict-free Replicated Data Types) to automatically merge concurrent edits from multiple offline devices without human intervention. For example, if two field technicians update the same work order while both offline, CRDTs apply deterministic merge rules (last-writer-wins for scalar values, union for sets, ordered-list merging for notes) to produce a consistent result when both devices reconnect. PWAs are installable directly from the browser, no App Store required, which eliminates Apple's 30% commission and Google's review process. For enterprises with 500+ field workers, this saves $150K-$300K annually in app store fees alone.