When Dockstore was created, CWL was the first descriptor language we supported. CWL has a very clear distinction between a tool and a workflow. However, our definition for each does not completely align with the language’s specification – strictly speaking, a CWL CommandLineTool does not require a Docker image, but we required tools to be associated with a Docker image on Dockstore. Furthermore, while WDL does not have separate concepts for tools and workflows, we still maintained a distinction between a tool and a workflow for WDL for legacy reasons.