The Visual Studio SDK helps you extend Visual Studio features or integrate new features into Visual Studio. You can distribute your extensions to other users, as well as to the Visual Studio Marketplace. The following are some of the ways in which you can extend Visual Studio:
Add commands, buttons, menus, and other UI elements to the IDE
Add tool windows for new functionality
Extend IntelliSense for a given language, or provide IntelliSense for new programming languages
Use light bulbs to provide hints and suggestions that help developers write better code
Enable support for a new language
Add a custom project type
Reach millions of developers via the Visual Studio Marketplace
The Visual Studio SDK is an optional feature in Visual Studio setup. You can also install the VSSDK later on. For more information, see Install the Visual Studio SDK.
You can find open source examples of VSSDK extensions on GitHub at Visual Studio Samples. This GitHub repo contains samples that illustrate various extensible features in Visual Studio.