This is a neat idea; it's sort of an entity-relationship diagram or class diagram for API resources. In fact, if your audience is familiar with these sorts of

This is a neat idea; it's sort of an entity-relationship diagram or class diagram for API resources. In fact, if your audience is familiar with these sorts of diagrams, I wonder if it'd be more readily scannable if you denoted the cardinality of the relationships with the sort of notation you'd see in ERDs or CDs? (Personally, I'm a big fan of Crow's Foot.)