Besides CWL, you can also describe tools via the WDL language. WDL does not directly have the concept of a Tool built in to the language like CWL. Instead, we define a tool as a one task WDL workflow, where the task has an associated Docker image.
This is a companion discussion topic for the original entry at https://docs.dockstore.org/docs/prereqs/getting-started-with-wdl/?source=post_page---------------------------