Firebase Realtime Database

Firebase Realtime Database is a cloud-hosted NoSQL database that syncs data between clients in real-time using a WebSocket connection. Data is stored as JSON and automatically synchronized to every connected client. It's tightly integrated with the Firebase ecosystem, making it incredibly fast to prototype real-time apps without backend code. However, its data model can lead to inefficient queries at scale, and costs are based on simultaneous connections and data transfer, which can be unpredictable.

It's often superseded for new projects by Firestore, which offers more structured queries.