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)

    return mcp.NewToolResultText(content), nil
}

Explanations

It's really very simple. My server will provide only one tool. The code implements a server that exposes a web "fetching" tool based on curl using the Model Control Protocol.

• First, I create an MCP server named mcp-curl version 1.0.0 that works with standard input/output (stdio)
• Then I define a tool named use_curl that takes a required url parameter
• Finally, I add the handler for this tool that executes the curl command with the -s option to retrieve the webpage content
• Of course, I handle errors and return the webpage content as text

Packaging the MCP Server with Docker

To make my life easier, I'll use a Dockerfile to build a Docker image containing my MCP server. This way, I can more easily deploy it on different platforms or make it available to anyone who wants to use it.

Dockerfile:

FROM golang:1.23.4-alpine AS builder
WORKDIR /app
COPY go.mod .
COPY main.go .

RUN