Creating an MCP Server in Go and Serving it with Docker

Introduction

Today we’ll look at how to create an MCP server in Go and serve it with Docker.

Prerequisites: having read Understanding the Model Context Protocol (MCP)

To write an MCP server, there are several official SDKs:

• TypeScript SDK
• Python SDK
• Kotlin SDK

In recent years, I’ve developed an appetite for Go, so I looked around to see if there was a Go implementation. On this page https://github.com/punkpeye/awesome-mcp-servers?tab=readme-ov-file#frameworks, I found several, notably https://github.com/mark3labs/mcp-go, by the creator of mcphost (which I discuss and use in the previous blog post).

The advantage of the mcp-go project is that it’s simple and also provides tools to develop an MCP client, which will be very useful for a future blog post.

Creating an MCP Server

I won’t detail or implement all the possibilities of an MCP server here. I’ll just implement the essentials:

• Provide a list of tools for the LLM
• Execute these tools when the LLM invokes them

When I use an LLM, there’s one thing I’d like to be able to do: give it a website link so it can find information there, make a summary for me, etc.

So I created an MCP server that calls the curl utility with a URL parameter and returns its content. But let’s look at the source code:

go.mod:

module mcp-curl

go 1.23.4

require github.com/mark3labs/mcp-go v0.8.2
require github.com/google/uuid v1.6.0

main.go:

package main

import (
	"context"
	"fmt"
	"os/exec"

	"github.com/mark3labs/mcp-go/mcp"
	"github.com/mark3labs/mcp-go/server"
)

func main() {
	// Create MCP server
	s := server.NewMCPServer(
		"mcp-curl",
		"1.0.0",
	)

	// Add a tool
	tool := mcp.NewTool("use_curl",
		mcp.WithDescription("fetch this webpage"),
		mcp.WithString("url",
			mcp.Required(),
			mcp.Description("url of the webpage to fetch"),
		),
	)

	// Add a tool handler
	s.AddTool(tool, curlHandler)

	fmt.Println("🚀 Server started")
	// Start the stdio server
	if err := server.ServeStdio(s); err != nil {
		fmt.Printf("😡 Server error: %v\n", err)
	}
	fmt.Println("👋 Server stopped")
}

func curlHandler(ctx context.Context, request mcp.CallToolRequest) (*mcp.CallToolResult, error) {

	url, ok := request.Params.Arguments["url"].(string)
	if !ok {
		return mcp.NewToolResultError("url must be a string"), nil
	}
	cmd := exec.Command("curl", "-s", url)
	output, err := cmd.Output()
	if err != nil {
		return mcp.NewToolResultError(err.Error()), nil
	}
	content := string(output)