There are two tools that you need to develop apps with Expo: a local development tool and a mobile client to open your app.
Local Development Tool: Expo CLI
Expo CLI is a tool for developing apps with Expo. In addition the command-line interface (CLI) it also has a graphical UI, Expo Developer Tools, that pops up in your web browser. With Expo Dev Tools you can quickly set up your test devices, view logs and more.
Expo client helps view your projects while you're developing them. When you serve your project with Expo CLI, it generates a development URL that you can open in Expo client to preview your app. On Android, Expo client can also be used to view others' projects on expo.io. Expo client works on devices, simulators, and emulators.
Required Android and iOS versions: The minimum Android version Expo supports is Android 5 and the minimum iOS version is iOS 10.0.
You don't need to manually install the Expo client on your emulator/simulator, because Expo CLI will do that automatically. See the next sections of this guide.
Install Xcode through the Apple App Store. It'll take a while, go have a nap. Next, open up Xcode, go to preferences and click the Components tab, install a simulator from the list.
Once the simulator is open and you have a project open in Expo Dev Tools, you can press Run on iOS simulator in Expo Dev Tools and it will install the Expo client to the simulator and open up your app inside of it. Read more about the iOS simulator.
Not working? Occasionally Expo CLI will have trouble installing the Expo client automatically, usually due to annoying small differences in your environment or Xcode toolchain. If you need to install the Expo client on your simulator manually, you can follow these steps:
Once the emulator is open and you have a project open in Expo Dev Tools, you can press Run on Android device/emulator in Expo Dev Tools and it will install the Expo client to the emulator and open up your app inside of it.
Some macOS users encounter issues if they do not have this installed on their machine, so we recommend that you install Watchman. Watchman watches files and records when they change, then triggers actions in response to this, and it's used internally by React Native. Download and install Watchman.