Hello World - MCP Server in Go

Introduction

This example demonstrates how to build a minimal Model Context Protocol (MCP) server in Go, using the mcp-go SDK. MCP is a lightweight JSON‑RPC‑based protocol that lets language model clients discover and invoke external tools in a structured way.

With just a few lines of Go code, you can:

Define an MCP server with a human‑readable name and version.
Declare one or more tools (commands) with typed parameters and descriptions.
Register handler functions that execute your custom logic when a client calls a tool.
Expose the server over standard I/O (stdin/stdout) so any MCP‑compatible client (like Cursor, Claude Desktop, or other IDE extensions) can launch and communicate with it without extra setup.

How It Works

Server Initialization
```
mcpServer := server.NewMCPServer(
  "Hello World MCP Server",
  "1.0.0",
  server.WithToolCapabilities(false),
)
```
- Creates an MCP server named “Hello World MCP Server” at version 1.0.0.
- Disables automatic tool capability announcements (so only your explicit tools appear).

Tool Definition

helloWorldTool := mcp.NewTool("hello_world",
  mcp.WithDescription("Greet someone"),
  mcp.WithString("name",
   mcp.Required(),
   mcp.Description("Person’s name"),
  ),
)

Defines a hello_world tool that accepts a single required string parameter name.
Descriptions help clients display usage information and generate prompts.

Handler Registration

mcpServer.AddTool(helloWorldTool, func(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
  name, ok := req.Params.Arguments["name"].(string)

  if !ok {
   return nil, errors.New("name must be a string")
  }

  return mcp.NewToolResultText(fmt.Sprintf("Hello, %s!", name)), nil
})

Associates the hello_world tool with a Go function.
Extracts the name argument, validates it, and returns a greeting.
Errors are surfaced back to the client as JSON‑RPC errors.

Serving Over Stdio
```
if err := server.ServeStdio(mcpServer); err != nil {
 fmt.Printf("Server error: %v\n", err)
}
```
- Starts an event loop reading JSON‑RPC requests from stdin and writing responses to stdout.
- Allows any MCP client to launch the binary directly and speak MCP over pipes.

Getting Started

Install Dependencies
```
go mod tidy
```
Build the Server
```
go build -o hello-mcp ./src/main.go
```
Connect from an MCP Client
- In your client’s configuration, point to the hello-mcp executable.
- The client will automatically discover the hello_world tool schema and let you invoke it.
Example:
```
{
  "mcpServers": {
    "demo-go-mcp": {
      "command": "path-to-server/hello-mcp"
    }
  }
}
```
or, use my MCP client made in Go

Enjoy building more complex workflows by adding additional tools, parameters, and transports (e.g., HTTP/SSE) as needed!

lucasgdb/mcp-server-go-example

Hello World - MCP Server in Go

Introduction

How It Works

Getting Started