---
title: Introducing Expo Atlas
authors: Cedric van Putten
published: May 23, 2024
categories: Development
---

Our goal at Expo is to create the best possible way to make apps. We are doing that through tooling that leverages the best of native and the most cutting-edge web patterns. By doing so, our framework became inherently more complicated. But, thanks to internal tooling, we are innovating our tooling faster than ever, introducing Expo Atlas.

Expo Atlas started as an internal tool to help us gain visibility into the more opaque parts of React Native development. The tool gives an excellent overview of the bundle, source and output code for individual modules, and each platform's dependency graph. And now we are shipping it to everyone.

![Expo Atlas. Visualize and understand your bundle output, easily spot optimization opportunities, iterate faster at scale.](https://cdn.sanity.io/images/9r24npb8/production/a6d505bb73449b4d71ee8cbcb4207c7384107433-887x576.gif)

Our Metro fast resolver is one of these new features, accelerated through Expo Atlas. The profiler in the Chrome Devtools helped us confirm that the default resolver is taking longer than it should be, and Expo Atlas helped us validate different approaches. We also have improved our Babel configuration to leverage more Hermes-supported language features, removing unnecessary transformations. Even early external testers, like [Backpack](https://twitter.com/backpack), decreased their JS bundle size by ±38% in just under 2 days.

## Built-in with Expo SDK 51

Expo Atlas works with `expo start` and `expo export` starting from Expo SDK 51. You can enable Atlas by setting the `EXPO_UNSTABLE_ATLAS=true` environment variable.

- Using Atlas with `expo start`, you can open Atlas through the more tools option in the CLI — `shift+m` — or just by opening [http://localhost:8081/_expo/atlas](http://localhost:8081/_expo/atlas). After launching your app on Android, iOS, or the web, Atlas provides you with all the information for each platform.
- Using Atlas with `expo export`, Expo exports a **.expo/atlas.jsonl** file. This file contains all bundle information, including actual source code. You can share or open this file with `npx expo-atlas .expo/atlas.jsonl`

Go ahead and try it today! We are excited to ship this tool to the whole community and can't wait to see what you'll do with Atlas.