Firebase vs Realm: What are the differences?

Firebase: The Realtime App Platform. Firebase is a cloud service designed to power real-time, collaborative applications. Simply add the Firebase library to your application to gain access to a shared data structure; any changes you make to that data are automatically synchronized with the Firebase cloud and with other clients within milliseconds; Realm: Realm makes it easy to build reactive apps, realtime collaborative features, and offline-first experiences. The Realm Mobile Platform is a next-generation data layer for applications. Realm is reactive, concurrent, and lightweight, allowing you to work with live, native objects.

Firebase and Realm are primarily classified as "Realtime Backend / API" and "Mobile Database" tools respectively.

Some of the features offered by Firebase are:

• Add the Firebase library to your app and get access to a shared data structure. Any changes made to that data are automatically synchronized with the Firebase cloud and with other clients within milliseconds.
• Firebase apps can be written entirely with client-side code, update in real-time out-of-the-box, interoperate well with existing services, scale automatically, and provide strong data security.
• Data Accessibility- Data is stored as JSON in Firebase. Every piece of data has its own URL which can be used in Firebase's client libraries and as a REST endpoint. These URLs can also be entered into a browser to view the data and watch it update in real-time.

On the other hand, Realm provides the following key features:

• Feels like Home - Realm’s data structures look like the Objects and Arrays of your language, but provide additional features such as: querying, relationships & graphs, thread safety, and more.
• Memory-Efficient - Realm is not built on SQLite. Instead, a custom C++ core is used to provide memory-efficient access to your data by using Realm objects, which usually consume less RAM than native objects.
• F-F-Fast! - Realm offers extraordinary performance compared to SQLite and other persistence solutions.

"Realtime backend made easy" is the top reason why over 318 developers like Firebase, while over 4 developers mention "Good" as the leading cause for choosing Realm.

Realm is an open source tool with 13.3K GitHub stars and 1.73K GitHub forks. Here's a link to Realm's open source repository on GitHub.

Instacart, 9GAG, and Twitch are some of the popular companies that use Firebase, whereas Realm is used by SocialCops, Patreon, and Wongnai. Firebase has a broader approval, being mentioned in 859 company stacks & 997 developers stacks; compared to Realm, which is listed in 39 company stacks and 5 developer stacks.