Developers can use the iOS software development kit (SDK) to create applications for Apple mobile devices. The SDK includes tools and interfaces for developing, installing, running and testing apps. Native apps can be written using the iOS system frameworks and the Objective-C programming language. Included in the iOS SDK are Xcode Tools, which include an integrated development environment (IDE) for managing application projects, a graphical tool for creating the user interface and a debugging tool for analyzing runtime performance. It also includes an iOS simulator, which allows developers to test apps on a Mac, and an iOS developer library, which provides all the necessary documentation and reference material.