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
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