ReSharper by Language: Google Protocol Buffers (Protobuf)
ReSharper highlights language syntax in .proto files, detects and highlights errors. Basic code completion and other typing assistance features are available in the editor. You can go to declarations of types and values, search for their usages, and enjoy other navigation features. You can also reformat Protobuf code and rename symbols.
For the full list of supported features, see ReSharper Features in Different Languages.