TFS variables across multiple build definitions

Question

How can I define variables in Team Foundation Server 2015 which are available across multiple build definitions for one project?

This is needed for a build number which is incremented every build and must be unique across multiple build definitions.

Answer 1

As the build ID is unique, instead of defining variables across multiple build definitions, you can simply specify the Build number format to $(date:yyyyMMdd).$(BuildId), check the screenshot below:

In this way, you'll get increased build number in multiple build definition: