What are the Azure DevOps System Variables?

Azure DevOps comes with a lot of system variables that can provide useful information to your pipelines.

Useful system variables

A quick list of useful system variables is below.

Variable Name	Variable Description
Agent.Name	The name of the agent that is registered with the pool If you are using a self-hosted agent, this name is specified by you. This variable is useful when using on-premise agents.
Agent.OS	The operating system of the agent host
Build.BuildNumber	The name of the completed build, also known as the run number
Build.SourceBranch	The branch of the triggering repo the build was queued for
System.DefaultWorkingDirectory	The local path on the agent where your source code files are downloaded
Common.TestResultsDirectory	The local path on the agent where the test results are created
Agent.MachineName	The name of the machine on which the agent is installed.
Agent.JobStatus	The status of the build.
System.AccessToken	A special variable that carries the security token used by the running build
System.Debug	Set this variable to true for debugging pipeline issues.

For the complete list, please refer to this link.