How to Create a Custom MCP Tool

Build your own Model Context Protocol (MCP) compatible tools

This guide shows you how to create a new custom tool that’s compatible with the Model Context Protocol (MCP) in gomcptest.

Prerequisites

  • A working installation of gomcptest
  • Go programming knowledge
  • Understanding of the MCP protocol basics

Steps to create a custom tool

1. Create the tool directory structure

mkdir -p tools/YourToolName/cmd

2. Create the README.md file

Create a README.md in the tool directory with documentation:

touch tools/YourToolName/README.md

Include the following sections:

  • Tool description
  • Parameters
  • Usage notes
  • Example

3. Create the main.go file

Create a main.go file in the cmd directory:

touch tools/YourToolName/cmd/main.go

4. Implement the tool functionality

Here’s a template to start with:

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"os"

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

// Define your tool's parameters structure
type Params struct {
	// Add your parameters here
	// Example:
	InputParam string `json:"input_param"`
}

func main() {
	server := mcp.NewServer()

	// Register your tool function
	server.RegisterFunction("YourToolName", func(params json.RawMessage) (any, error) {
		var p Params
		if err := json.Unmarshal(params, &p); err != nil {
			return nil, fmt.Errorf("failed to parse parameters: %w", err)
		}

		// Implement your tool's logic here
		result := doSomethingWithParams(p)

		return result, nil
	})

	if err := server.Run(os.Stdin, os.Stdout); err != nil {
		log.Fatalf("Server error: %v", err)
	}
}

func doSomethingWithParams(p Params) interface{} {
	// Your tool's core functionality
	// ...
	
	// Return the result
	return map[string]interface{}{
		"result": "Your processed result",
	}
}

5. Add the tool to the Makefile

Open the Makefile in the root directory and add your tool:

YourToolName:
	go build -o bin/YourToolName tools/YourToolName/cmd/main.go

Also add it to the all target.

6. Build your tool

make YourToolName

7. Test your tool

Test the tool directly:

echo '{"name":"YourToolName","params":{"input_param":"test"}}' | ./bin/YourToolName

8. Use with the CLI

Add your tool to the CLI command:

./bin/cliGCP -mcpservers "./GlobTool;./GrepTool;./LS;./View;./YourToolName;./dispatch_agent;./Bash;./Replace"

Tips for effective tool development

  • Focus on a single, well-defined purpose
  • Provide clear error messages
  • Include meaningful response formatting
  • Implement proper parameter validation
  • Handle edge cases gracefully
  • Consider adding unit tests in a _test.go file

Dernière modification 18.03.2025: ok (fd154af)