iOS Simulator

The iOS Simulator is a macOS app shipped with Xcode that runs iPhone, iPad and other Apple device builds on your Mac. It is where most React Native iOS development happens day to day, launched by npx expo run:ios or npx react-native run-ios.

It is a simulator, not an emulator: it does not imitate iPhone hardware. Your app is compiled for the Mac’s own CPU against a simulator SDK and runs as a Mac process. That has practical consequences:

• It only exists on macOS. There is no official way to run it on Windows or Linux.
• Simulator builds cannot be installed on a phone, and device builds cannot run in the Simulator. A development build made for one will not work on the other.
• Performance is not representative. A fast Mac hides jank that a three-year-old iPhone will show, so profile on real hardware.
• localhost is your Mac, which is why the app reaches Metro with no extra setup, unlike the Android Emulator.

Handy shortcuts: Cmd+D opens the Dev Menu, Cmd+R reloads, and Cmd+Shift+H goes to the home screen. The xcrun simctl command line tool can boot devices, open URLs to test deep links, grant permissions and send a fake push payload.

The common misconception is that "it works in the Simulator" means it works on a device. Camera hardware, some sensors, real push delivery, Face ID behaviour, signing and entitlements, and memory limits all differ. Test anything touching those on a physical iPhone before release.