The Windows Software Development Kit (SDK) for Windows 8.1 contains headers, libraries, and tools you can use when you create apps that run on Windows operating systems.
Updated APIs are listed in the Win32 and COM for Windows Runtime apps reference.
The latest version of the Windows App Certification Kit is an in-place update for all earlier versions.
Version 3.3 introduces support for pre-certification testing of Windows 8.1 Phone apps prior to the final Windows Phone Store submission.
You must install a compiler and build environment separately.
If you require a complete development environment that includes compilers and a build environment, you can download Visual Studio 2013, which includes the appropriate components of the Windows SDK.
To download the SDK and install it on another computer, click the download link and run the setup.
Then in the Specify Location dialog box, click Download the Windows Software Development Kit for installation on a separate computer.
Install and download Threading APIs are now available for use with Windows Store and Windows Phone apps.
For a full list of Win32 APIs supported by Windows Store apps, see Win32 and COM for Windows Runtime apps reference.