Instruments is an application that comes bundled with the iPhone SDK, so you already have it installed if you have the SDK installed. As mentioned earlier, Instruments is great for seeing an overview of what your application is doing while running. You can see how much memory and CPU you’re using, and it can even identify leaks for you.
Unlike Clang, Instruments works by analyzing the application while it is running. You can have Instruments analyze your app while it runs either in the iPhone Simulator or on a real device.
Instruments is launched like any other Mac application, either via Spotlight or from the application’s location on disk. By default, the application is located in /Developer/ Applications. ...