-Here: https://hibernate.org/orm/tooling/
-as here: https://github.com/hibernate/hibernate-metamodelgen

Both link to:
The first links to: https://docs.jboss.org/hibernate/orm/6.1/topical/html_single/metamodelgen/MetamodelGenerator.html
The latter to: http://docs.jboss.org/hibernate/stable/orm/topical/html/metamodelgen/MetamodelGenerator.html

Better proposal:
https://docs.jboss.org/hibernate/orm/6.1/userguide/html_single/Hibernate_User_Guide.html#tooling