protobuf-dt is Google’s Eclipse-based editor for protocol buffers. It provides all the features you’d expect from an Eclipse editor (syntax highlighting, outline view, content assist, etc.) plus some protocol buffer-specific features, such as "Open Declaration" (hyperlinking) support, including imported .proto files, configurable integration with protoc, and automatic removal of trailing whitespace.

URL: protobuf-dt - Google's Eclipse-based Development Environment for Protocol Buffers - Google Project Hosting