Extensions for Visual Studio Online, REST APIs for TFS 2015 RC, and more from Build 2015

This post announces the early preview of a new extensibility model for Visual Studio Online (VSO) called extensions, enabling first-class, seamless connections between VSO and other tools and services, with integration points within the web experience such as context menus, toolbars, and new hubs. It also announces the availability of REST APIs for TFS 2015 RC, which can be called on both TFS and VSO, and the availability of service hooks in TFS 2015 RC for integration with various services. The MSDN API Sandbox is introduced as a tool for trying out VSO REST APIs with C# code samples.