UML Class Diagrams

What language does this apply to? If it's a proto syntax change, is it for proto2 or proto3? proto3 If it's about generated code change, what programming language? any

Describe the problem you are trying to solve.

It would be very useful to generate class diagrams based on protobuf message definitions, including the members/fields of each class, as well as the class relationships.

Describe the solution you'd like

A script or command-line utility to output images (e.g. png) or something like GraphViz files with the generated UML diagrams.

Describe alternatives you've considered

I've looked into protoc-gen-uml and protobuf2uml but both tools lack useful documentation and neither are actively maintained.