The Simulator app helps you rapidly prototype and test builds of your app in different runtimes during the development process. Installed as part of Xcode, Simulator runs on your Mac and enables you to simulate iOS, tvOS, and watchOS devices running current and some legacy operating systems. You can run your app in Simulator by choosing a simulated device in the scheme pop-up menu in the toolbar, or by choosing Xcode > Open Developer Tool > Simulator.