Sample MCP Server - Stdio Transport

A Model Context Protocol (MCP) server implementation using stdio (standard input/output) transport. This server provides utility tools for text processing, currency formatting, and unit conversions.

Features

Available Tools

1. word_count - Analyze text and count words, characters, and lines

   • Input: text (string)
   • Output: Word count, character count, character count without whitespace, line count

2. format_currency - Format numbers as currency with proper symbols and decimal places

   • Input: amount (number), currency (USD, EUR, GBP, or JPY)
   • Output: Formatted currency string (e.g., "$123.45", "¥1234")

3. slugify - Convert text to URL-friendly slugs

   • Input: text (string)
   • Output: Lowercase, hyphen-separated slug with no special characters

4. roman_numeral - Convert between decimal numbers (1-3999) and Roman numerals

   • Input: Either number (1-3999) or roman (Roman numeral string)
   • Output: Converted value (Roman numeral or decimal number)

5. temperature_convert - Convert temperatures between Celsius, Fahrenheit, and Kelvin

   • Input: value (number), from_unit (celsius/fahrenheit/kelvin), to_unit (celsius/fahrenheit/kelvin)
   • Output: Converted temperature value

Requirements

• Go 1.23 or later
• Docker (for containerization)
• Kubernetes cluster (for deployment)

Transport: Stdio

This server uses stdio transport, which communicates through standard input and output streams. This is ideal for:

• Local command-line tools
• Process-to-process communication
• Shell script integration
• IDE integrations
• Desktop applications

Unlike HTTP-based transports (SSE, Streamable HTTP), stdio provides:

• Lower overhead (no HTTP layer)
• Direct process communication
• Natural fit for CLI tools
• Simpler deployment for local use

Quick Start

Using MCP Inspector (Recommended for Testing)

The MCP Inspector is the official debugging tool for MCP servers:

# Install the inspector globally
npm install -g @modelcontextprotocol/inspector

# Run the inspector with this server
npx @modelcontextprotocol/inspector go run main.go

This will:

1. Start your MCP server as a subprocess
2. Open a web interface at http://localhost:5173
3. Allow you to test all tools interactively

Using with Claude Desktop

Add this server to your Claude Desktop configuration:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "stdio-tools": {
      "command": "go",
      "args": ["run", "/path/to/sample-mcp-server-stdio/main.go"]
    }
  }
}

Or if you've built the binary:

{
  "mcpServers": {
    "stdio-tools": {
      "command": "/path/to/mcp-server-stdio"
    }
  }
}

Building the Binary

# Build for your current platform
go build -o mcp-server-stdio

# Build for Linux
GOOS=linux GOARCH=amd64 go build -o mcp-server-stdio

# Run the binary
./mcp-server-stdio

Using the Tools

Example: Word Count

{
  "method": "tools/call",
  "params": {
    "name": "word_count",
    "arguments": {
      "text": "Hello world!\nThis is a test."
    }
  }
}

Response:

Words: 5
Characters: 29
Characters (no whitespace): 24
Lines: 2

Example: Format Currency

{
  "method": "tools/call",
  "params": {
    "name": "format_currency",
    "arguments": {
      "amount": 1234.56,
      "currency": "USD"
    }
  }
}

Response: $1234.56

Example: Slugify

{
  "method": "tools/call",
  "params": {
    "name": "slugify",
    "arguments": {
      "text": "Hello World! This is a Test."
    }
  }
}

Response: hello-world-this-is-a-test

Example: Roman Numeral Conversion

Convert to Roman:

{
  "method": "tools/call",
  "params": {
    "name": "roman_numeral",
    "arguments": {
      "number": 2024
    }
  }
}

Response: MMXXIV

Convert from Roman:

{
  "method": "tools/call",
  "params": {
    "name": "roman_numeral",
    "arguments": {
      "roman": "MMXXIV"
    }
  }
}

Response: 2024

Example: Temperature Conversion

{
  "method": "tools/call",
  "params": {
    "name": "temperature_convert",
    "arguments": {
      "value": 100,
      "from_unit": "celsius",
      "to_unit": "fahrenheit"
    }
  }
}

Response: 212.00

Client Library Examples

TypeScript/JavaScript

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";

const transport = new StdioClientTransport({
  command: "./mcp-server-stdio",
  args: []
});

const client = new Client({
  name: "example-client",
  version: "1.0.0"
}, {
  capabilities: {}
});

await client.connect(transport);

// Use the word_count tool
const result = await client.callTool({
  name: "word_count",
  arguments: {
    text: "Hello world! This is a test."
  }
});

console.log(result);

Python

from mcp.client.stdio import stdio_client, StdioServerParameters
from mcp.types import CallToolRequest

server_params = StdioServerParameters(
    command="./mcp-server-stdio",
    args=[]
)

async with stdio_client(server_params) as (read, write):
    # Initialize the connection
    await write({"jsonrpc": "2.0", "method": "initialize", "params": {...}})

    # Call a tool
    result = await write(CallToolRequest(
        method="tools/call",
        params={
            "name": "slugify",
            "arguments": {"text": "Hello World!"}
        }
    ))

    print(result)

Docker Deployment

Build and Push Docker Image

# Build for linux/amd64 architecture
docker build -t aliok/sample-mcp-server-stdio:latest .

# Push to Docker Hub (or your registry)
docker push aliok/sample-mcp-server-stdio:latest

Note: Replace aliok with your Docker Hub username or registry path. The Dockerfile is configured to build for linux/amd64 architecture.

Run with Docker

Since stdio requires interactive terminal access:

docker run -i aliok/sample-mcp-server-stdio:latest

Note: Stdio servers in Docker are primarily useful for:

• Building and testing the container
• Using as a base for sidecar containers
• Integration into larger container orchestration systems

For typical MCP server deployments, consider HTTP-based transports (SSE or Streamable HTTP).

Kubernetes Deployment

While stdio transport can run in Kubernetes, it's less common than HTTP-based transports. The provided manifests demonstrate how to deploy stdio servers in K8s:

Deploy to Kubernetes

# Apply manifests
kubectl apply -f k8s/

Note: The deployment uses aliok/sample-mcp-server-stdio:latest. Update k8s/deployment.yaml if using a different registry.

Verify Deployment

# Check deployment status
kubectl get deployment sample-mcp-server-stdio

# Check pods
kubectl get pods -l app=sample-mcp-server-stdio

# View logs
kubectl logs -l app=sample-mcp-server-stdio

Access the Server

Since stdio servers communicate through stdin/stdout, you can interact with them using kubectl exec:

# Access the server interactively
kubectl exec -it deployment/sample-mcp-server-stdio -- /bin/sh

# Or pipe commands directly
echo '{"jsonrpc":"2.0","method":"initialize","params":{}}' | kubectl exec -i deployment/sample-mcp-server-stdio -- ./mcp-server-stdio

Note: For production Kubernetes deployments, consider using the SSE or Streamable HTTP variants which provide better HTTP-based access patterns.

Development

Project Structure

sample-mcp-server-stdio/
├── main.go              # Main server implementation
├── go.mod               # Go module definition
├── go.sum               # Dependency checksums
├── Dockerfile           # Container build configuration
├── .dockerignore        # Docker build exclusions
├── README.md            # This file
├── .claude/             # Claude IDE settings
│   └── settings.local.json
└── k8s/                 # Kubernetes manifests
    ├── deployment.yaml
    ├── service.yaml
    └── kustomization.yaml

Adding New Tools

To add a new tool:

1. Define the argument struct with JSON schema tags:

type MyToolArgs struct {
    Input string `json:"input" jsonschema:"description=Input description"`
}

1. Create the handler function:

func handleMyTool(ctx context.Context, req *mcp.CallToolRequest, args MyToolArgs) (*mcp.CallToolResult, any, error) {
    // Your tool logic here
    return &mcp.CallToolResult{
        Content: []any{
            mcp.TextContent{
                Type: "text",
                Text: "result",
            },
        },
    }, nil, nil
}

1. Register the tool in main():

mcp.AddTool(server, "my_tool", "Tool description",
    jsonschema.For[MyToolArgs](),
    handleMyTool)

Logging

All logs are written to stderr to keep stdout clean for MCP protocol messages. Log format:

[YYYY-MM-DD HH:MM:SS.mmmmmm] [TAG] message

Log tags:

• [MAIN] - Server lifecycle events
• [TOOL] - Tool execution
• [ERROR] - Error messages

Dependencies

• Go SDK: github.com/modelcontextprotocol/go-sdk v1.2.0
• JSON Schema: github.com/google/jsonschema-go v0.3.0

Related Implementations

• sample-mcp-server-sse: Server using Server-Sent Events (SSE) transport
• sample-mcp-server-streamable-http: Server using Streamable HTTP transport

Each transport has different use cases:

• Stdio: Local tools, CLI integration, desktop apps
• SSE: Real-time streaming, web applications, push notifications
• Streamable HTTP: Traditional request/response, REST-like APIs

License

This is a sample implementation for educational purposes.

Learn More

• Model Context Protocol Documentation
• MCP Specification
• MCP TypeScript SDK
• MCP Python SDK
• MCP Go SDK