Firebase is a comprehensive mobile and web development platform that provides a variety of tools and services for building, managing, and scaling apps. Some features of Firebase are free to use, while others are available for a fee.

The following Firebase features are available for free:

• Realtime Database: A cloud-hosted NoSQL database that allows you to store and sync data in real-time.
• Cloud Firestore: A flexible, scalable NoSQL cloud database that stores and syncs data in real-time.
• Cloud Functions: A serverless platform that lets you run your code in response to events and automatically scales to meet demand.
• Firebase Hosting: A static and dynamic web hosting platform that serves your content globally.
• Firebase Authentication: A backend service that allows you to authenticate users and manage user accounts.
• Firebase Crashlytics: A crash reporting service that helps you track, prioritize, and fix stability issues that affect your users.

Some other features of Firebase, such as Cloud Storage and Firebase ML, are available for a fee. You can view the pricing details for these and other Firebase features on the Firebase pricing page.