Understanding and comparing fingerprints in Expo apps

TL;DR: Expo SDK 52 introduced automatic fingerprinting for builds and updates, helping ensure compatibility between your native code and JS bundle. New CLI tools (eas fingerprint:generate and eas fingerprint:compare) make it easy to track native layer changes and avoid crashes from mismatches. In this blog I'll quickly show you how to use these new tools.

A fingerprint is a unique hash representing the native dependencies of your Expo application. It ensures compatibility between the native layer and the JavaScript layer of your app. By default, Expo calculates fingerprints by hashing your app's dependencies, custom native code, native project files, and configurations. Starting with Expo SDK 52, fingerprints are now automatically calculated for every build and update, providing increased visibility into your app's native layer.

Fingerprints play a crucial role in maintaining app compatibility. By representing the state of your native dependencies, fingerprints help you identify if your JavaScript updates are compatible with existing native binaries, preventing potential crashes caused by mismatches.

For example, if you updated your JavaScript code to start using expo-camera, but you forgot to rebuild the native binary with the updated dependency, the app would crash when users open the camera because your last build doesn't include the native code for expo-camera.

With fingerprints, you’d immediately notice the mismatch between your JavaScript and native layers, and then you'd rebuild the app before deploying the update.

There are tons of different scenarios where fingerprints can save you from a crash. It doesn't take much imagination to think of them because we've all been there!

The new eas fingerprint:generate command allows you to create a fingerprint from your local project directory and upload it directly to Expo servers for easy access and comparison:

For detailed insights or integration into automated workflows, use the --json flag to output the raw fingerprint.

We've introduced a new CLI command, eas fingerprint:compare, enabling you to easily detect differences in fingerprints between builds, updates, or your local project directory. This tool simplifies debugging by clearly showing you how your native layers differ.

Here's how you can use it:

You can also click the "Compare" button in the Expo website to generate and view a clear diff of your native layers.

With automatic fingerprinting in Expo SDK 52 and new CLI tools like eas fingerprint:generate and eas fingerprint:compare, you now have deeper insight and greater control over your app’s native layer. These features reduce guesswork, improve stability, and make it easier to debug, collaborate, and ship updates confidently. Whether you're working solo or across large teams, fingerprints help ensure that your JavaScript and native code stay in sync—so your users get the best possible experience, every time.

Give it a try and let us know what you think!