MCP Go SDK

A Go implementation of the Model Context Protocol (MCP), providing both client and server capabilities for integrating with LLM surfaces.

Overview

The Model Context Protocol allows applications to provide context for LLMs in a standardized way, separating the concerns of providing context from the actual LLM interaction. This Go SDK implements the full MCP specification, making it easy to:

• Build MCP clients that can connect to any MCP server
• Create MCP servers that expose resources, prompts and tools
• Use standard transports like stdio and SSE (coming soon)
• Handle all MCP protocol messages and lifecycle events

A small example

Curious what all this looks like in practice? Here's an example server that exposes the contents of an io.FS as resources.

package main

import (
	"context"
	"flag"
	"io/fs"
	"log"
	"mime"
	"os"
	"path/filepath"
	"strings"

	"github.com/riza-io/mcp-go"
)

type FSServer struct {
	fs fs.FS

	mcp.UnimplementedServer
}

func (s *FSServer) Initialize(ctx context.Context, req *mcp.Request[mcp.InitializeRequest]) (*mcp.Response[mcp.InitializeResponse], error) {
	return mcp.NewResponse(&mcp.InitializeResponse{
		ProtocolVersion: req.Params.ProtocolVersion,
		Capabilities: mcp.ServerCapabilities{
			Resources: &mcp.Resources{},
		},
	}), nil
}

func (s *FSServer) ListResources(ctx context.Context, req *mcp.Request[mcp.ListResourcesRequest]) (*mcp.Response[mcp.ListResourcesResponse], error) {
	var resources []mcp.Resource
	fs.WalkDir(s.fs, ".", func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if d.IsDir() {
			return nil
		}
		resources = append(resources, mcp.Resource{
			URI:      "file://" + path,
			Name:     path,
			MimeType: mime.TypeByExtension(filepath.Ext(path)),
		})
		return nil
	})
	return mcp.NewResponse(&mcp.ListResourcesResponse{
		Resources: resources,
	}), nil
}

func (s *FSServer) ReadResource(ctx context.Context, req *mcp.Request[mcp.ReadResourceRequest]) (*mcp.Response[mcp.ReadResourceResponse], error) {
	contents, err := fs.ReadFile(s.fs, strings.TrimPrefix(req.Params.URI, "file://"))
	if err != nil {
		return nil, err
	}
	return mcp.NewResponse(&mcp.ReadResourceResponse{
		Contents: []mcp.ResourceContent{
			{
				URI:      req.Params.URI,
				MimeType: mime.TypeByExtension(filepath.Ext(req.Params.URI)),
				Text:     string(contents), // TODO: base64 encode
			},
		},
	}), nil
}

func main() {
	flag.Parse()

	root := flag.Arg(0)
	if root == "" {
		root = "/"
	}

	server := mcp.NewStdioServer(&FSServer{
		fs: os.DirFS(root),
	})

	if err := server.Listen(context.Background(), os.Stdin, os.Stdout); err != nil {
		log.Fatal(err)
	}
}

You can compile this example and wire it up to Claude Desktop (or any other MCP client).

{
	"mcpServers": {
		"fs": {
			"command": "/path/to/mcp-go-fs",
			"args": [
				"/path/to/root/directory"
			]
		}
	}
}

Documentation

• Model Context Protocol documentation
• MCP Specification
• Example Servers

Roadmap

The majority of the base protocol is implemented. The following features are on our roadmap:

• Notifications
• Sampling
• Roots

Legal

Offered under the MIT license.