NoSQL document database with real-time sync, offline persistence, and security rules.

• Supports both Client SDK (authenticated users) and Admin SDK (server-side, bypasses rules) with modular v9+ API for CRUD, queries, transactions, and batch operations
• Real-time listeners via onSnapshot() for documents and collections; requires manual unsubscribe to prevent memory leaks and connection limits
• Compound queries with multiple filters, range queries, array operations, and pagination via cursor-based navigation; composite indexes required for complex queries
• Offline persistence with IndexedDB caching and multi-tab synchronization; handles pending writes and cache-vs-server data source detection
• Prevents 10 documented errors including permission-denied, missing indexes, invalid query combinations, listener memory leaks, and quota exhaustion