elm-protoc
Elm utility for generating Elm & Native JavaScript source for Google Protocol Buffers
First things first, if you're just interested in generating pure Elm JSON decoders/encoders from protocol buffer message definitions, shout out to https://github.com/tiziano88/elm-protobuf which is probably more appropriate for most projects
Architecture
elm-protoc is NOT a protoc plugin, but is rather a standalone app that uses protoc to produce JavaScript, and then generates Elm Types & to match your protobuf messages, and finally generates Elm functions (& Native modules bindings) for serializing the Elm value to/from the binary wire format.