SDK

Hop is a set of Java libraries before it is a GUI or a command line tool, so a pipeline or workflow can be executed from your own application.

The Hop SDK — initializing the API, plugin folders, metadata providers, variables, and running pipelines and workflows.

The Hop Server JSON API — the same capability over HTTP, when embedding the libraries is not an option.
How a pipeline and a workflow run — what the SDK is driving underneath.