WinRT

Windows Runtime, commonly known as WinRT, is a platform API and runtime introduced by Microsoft for building Windows Store apps. Debuted with Windows 8 in 2012 (and also shipped on Windows Phone 8.1), it provides a modern, security-conscious API surface that allows applications to access Windows features in a sandboxed environment while remaining language-agnostic.

WinRT is implemented as a runtime built on top of a COM-like infrastructure. API contracts are described with metadata files (with the .winmd extension) and exposed through a set of Windows namespaces such as Windows.Storage, Windows.Networking, and Windows.UI. The runtime supports language projections, enabling developers to write apps in multiple languages while consuming the same underlying APIs. Common projections exist for C++, C#, and VB.NET, as well as JavaScript for Web-based applications.

The API surface emphasizes asynchronous programming and modern UI capabilities. WinRT defines a rich set of APIs for file I/O, networking, sensors, multimedia, notifications, and user interface components, among others. It uses asynchronous operation patterns like IAsyncOperation and task-based equivalents in projections to promote responsive apps.

Applications built on WinRT are packaged as appx packages and run within a sandboxed app container with certain declared capabilities. This model supports security boundaries and easier deployment and updates across Windows devices. The Windows Runtime also serves as the foundation for the Universal Windows Platform (UWP), providing a unified API surface across devices; Windows 10 and later expanded the runtime with additional APIs and integration, while continuing to support existing WinRT components and language projections.