protoc-gen-go-mcp

protoc-gen-go-mcp is a Protocol Buffers compiler plugin that generates Model Context Protocol (MCP) servers for your gRPC or ConnectRPC APIs.

It generates *.pb.mcp.go files for each protobuf service, enabling you to delegate handlers directly to gRPC servers or clients. Under the hood, MCP uses JSON Schema for tool inputs—protoc-gen-go-mcp auto-generates these schemas from your method input descriptors.

⚠️ Currently supports mark3labs/mcp-go as the MCP server runtime. Future support is planned for official Go SDKs and additional runtimes.

✨ Features

• 🚀 Auto-generates MCP handlers from your .proto services
• 📦 Outputs JSON Schema for method inputs
• 🔄 Wire up to gRPC or ConnectRPC servers/clients
• 🧩 Easy integration with buf

🔧 Usage

Generate code

Add entry to your buf.gen.yaml:

...
plugins:
  - local:
      - go
      - run
      - github.com/redpanda-data/protoc-gen-go-mcp/cmd/protoc-gen-go-mcp@latest
    out: ./gen/go
    opt: paths=source_relative

You need to generate the standard *.pb.go files as well. protoc-gen-go-mcp by defaults uses a separate subfolder {$servicename}mcp, and imports the *pb.go files - similar to connectrpc-go. See here for a complete example.

After running buf generate, you will see a new folder for each package with protobuf Service definitions:

tree example/gen/
gen
└── go
    └── proto
        └── example
            └── v1
                ├── example.pb.go
                └── examplev1mcp
                    └── example.pb.mcp.go

Wiring Up MCP with gRPC server (in-process)

Example for in-process registration:

srv := exampleServer{} // your gRPC implementation

// Register all RPC methods as tools on the MCP server
examplev1mcp.RegisterExampleServiceHandler(mcpServer, &srv)

Each RPC method in your protobuf service becomes an MCP tool.

➡️ See the full example for details.

Wiring up with grpc and connectrpc client

It is also possible to directly forward MCP tool calls to gRPC clients.

examplev1mcp.ForwardToExampleServiceClient(mcpServer, myGrpcClient)

Same for connectrpc:

examplev1mcp.ForwardToConnectExampleServiceClient(mcpServer, myConnectClient)

This directly connects the MCP handler to the connectrpc client, requiring zero boilerplate.

⚠️ Limitations

• No interceptor support (yet). Registering with a gRPC server bypasses interceptors.
• Tool name mangling for long RPC names: If the full RPC name exceeds 64 characters (Claude desktop limit), the head of the tool name is mangled to fit.

🗺️ Roadmap

• Reflection/proxy mode
• Interceptor middleware support in gRPC server mode
• Support for the official Go MCP SDK (once published)

💬 Feedback

We'd love feedback, bug reports, or PRs! Join the discussion and help shape the future of Go and Protobuf MCP tooling.