Firebase Realtime Database

Firebase Realtime Database is Google's real-time JSON database. Data is synced across all connected clients via WebSockets. Write to database on phone A, phone B and web instantly see the change. No polling, no delay. Ideal for collaborative apps where millisecond latency matters: shared documents, live chat, multiplayer games, real-time notifications. Data is organized as JSON tree. Security Rules (JSON format) control who reads/writes what. Offline support built-in: edits queue locally, sync when online.