If you're extending Airflow 3.1+ with custom UI pages, FastAPI endpoints, or React components that live inside the Airflow process, this is the reference you need. It covers the full plugin system: mounting FastAPI apps, adding nav links and DAG tabs, serving static files, and calling the Airflow API from your plugin code. The critical bits are spelled out clearly: no Flask or flask_appbuilder (those are Airflow 2 patterns), always use relative paths in HTML and JavaScript or you'll break behind reverse proxies, and wrap any blocking calls in asyncio.to_thread(). The structure is practical, with file layout examples and a component decision table that maps what you want to build to the right plugin field.
npx skills add https://github.com/astronomer/agents --skill airflow-plugins