Building MCP Servers

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { z } from "zod";

// Create the MCP server
const server = new McpServer({
  name: "weather-server",
  version: "1.0.0",
  description: "A simple weather MCP server"
});

// Define a tool: get_weather
server.tool(
  "get_weather",
  "Get current weather for a city",
  {
    city: z.string().describe("City name"),
    units: z.enum(["celsius", "fahrenheit"])
           .optional()
           .default("celsius")
  },
  async ({ city, units }) => {
    // In production, call a real weather API here
    const temp = units === "celsius" ? "22°C" : "72°F";
    return {
      content: [{
        type: "text",
        text: `Weather in ${city}: ${temp}, partly cloudy`
      }]
    };
  }
);

// Define a resource: server info
server.resource(
  "server-info",
  "info://server",
  "Information about this MCP server",
  async () => ({
    contents: [{
      uri: "info://server",
      text: "Weather MCP Server v1.0.0 - Provides weather data",
      mimeType: "text/plain"
    }]
  })
);

// Define a prompt: weather_report
server.prompt(
  "weather_report",
  "Generate a weather report for a city",
  { city: z.string().describe("City name") },
  async ({ city }) => ({
    messages: [{
      role: "user",
      content: {
        type: "text",
        text: `Please generate a detailed weather report for ${city}. Use the get_weather tool to fetch current data, then provide a summary with recommendations.`
      }
    }]
  })
);

// Start the server with stdio transport
const transport = new StdioServerTransport();
await server.connect(transport);
console.error("Weather MCP server running on stdio");

pip install mcp

from mcp.server.fastmcp import FastMCP

# Create the MCP server
mcp = FastMCP("weather-server")

# Define a tool: get_weather
@mcp.tool()
def get_weather(city: str, units: str = "celsius") -> str:
    """Get current weather for a city.

    Args:
        city: City name to get weather for
        units: Temperature units (celsius or fahrenheit)
    """
    # In production, call a real weather API here
    temp = "22°C" if units == "celsius" else "72°F"
    return f"Weather in {city}: {temp}, partly cloudy"

# Define a resource: server info
@mcp.resource("info://server")
def server_info() -> str:
    """Information about this MCP server."""
    return "Weather MCP Server v1.0.0 - Provides weather data"

# Define a prompt: weather_report
@mcp.prompt()
def weather_report(city: str) -> str:
    """Generate a weather report for a city."""
    return f"Please generate a detailed weather report for {city}. " \
           f"Use the get_weather tool to fetch current data, " \
           f"then provide a summary with recommendations."

# Run the server
if __name__ == "__main__":
    mcp.run()

# TypeScript project
my-mcp-server/
  ├── src/
  │   ├── index.ts          # Server entry point
  │   ├── tools/             # Tool implementations
  │   │   ├── weather.ts
  │   │   └── search.ts
  │   ├── resources/         # Resource handlers
  │   │   └── files.ts
  │   └── prompts/           # Prompt templates
  │       └── report.ts
  ├── package.json
  ├── tsconfig.json
  └── README.md

# Python project
my-mcp-server/
  ├── server.py              # Server entry point
  ├── tools/                 # Tool implementations
  │   ├── weather.py
  │   └── search.py
  ├── resources/             # Resource handlers
  │   └── files.py
  ├── pyproject.toml
  └── README.md

server.tool(
  "read_file",
  "Read contents of a file",
  { path: z.string().describe("File path") },
  async ({ path }) => {
    try {
      const content = await fs.readFile(path, "utf-8");
      return {
        content: [{ type: "text", text: content }]
      };
    } catch (error) {
      return {
        content: [{
          type: "text",
          text: `Error reading file: ${error.message}`
        }],
        isError: true
      };
    }
  }
);

@mcp.tool()
def read_file(path: str) -> str:
    """Read contents of a file.

    Args:
        path: File path to read
    """
    try:
        with open(path, "r") as f:
            return f.read()
    except FileNotFoundError:
        raise ValueError(f"File not found: {path}")
    except PermissionError:
        raise ValueError(f"Permission denied: {path}")

# Install and run the MCP Inspector
npx @modelcontextprotocol/inspector

# Or test directly with a TypeScript server:
npx @modelcontextprotocol/inspector node dist/index.js

# Or test a Python server:
npx @modelcontextprotocol/inspector python server.py