Realtime Database

Firebase Realtime Database is a cloud-hosted NoSQL database that stores data as nested JSON and syncs changes to all connected clients in real-time over WebSockets. When one client writes data, all other clients receive the update within milliseconds automatically. No polling, no API calls, just declarative listeners that trigger callbacks on data changes. The database has a simple data model: start at a root path and nest objects and arrays beneath it. Access control is handled by security rules (a custom language that evaluates on the server). It's optimized for real-time collaboration and high-frequency updates.