Learn MCP

1. Client starts server process (stdio) or connects (SSE)
2. Client sends "initialize" request with protocol version
3. Server responds with capabilities (tools, resources, prompts)
4. Client sends "initialized" notification
5. Normal message exchange begins
6. Either side can send requests/notifications
7. Client sends "shutdown" or terminates the process

# macOS
~/Library/Application Support/Claude/claude_desktop_config.json

# Windows
%APPDATA%\Claude\claude_desktop_config.json

# Linux
~/.config/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/you/Projects"
      ]
    }
  }
}

mkdir my-mcp-server
cd my-mcp-server
npm init -y
npm install @modelcontextprotocol/sdk zod
npm install -D typescript @types/node
npx tsc --init

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

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

// Define a tool
server.tool(
  "get_weather",
  "Get the current weather for a city",
  {
    city: z.string().describe("City name (e.g., 'San Francisco')"),
    units: z.enum(["celsius", "fahrenheit"])
      .optional()
      .default("celsius")
      .describe("Temperature units"),
  },
  async ({ city, units }) => {
    // In a real server, you would call a weather API here.
    // This is a simplified example.
    const temp = units === "fahrenheit" ? 72 : 22;
    const description = "Partly cloudy";

    return {
      content: [
        {
          type: "text",
          text: `Weather in ${city}: ${temp}${
            units === "fahrenheit" ? "F" : "C"
          }, ${description}`,
        },
      ],
    };
  }
);

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

main().catch(console.error);

# Build the project
npx tsc

# The compiled output will be in the build/ directory
# (or wherever your tsconfig.json outDir points)

// Static resource
server.resource(
  "project-readme",
  "file:///project/README.md",
  async (uri) => ({
    contents: [
      {
        uri: uri.href,
        text: "# My Project\nThis is the readme content...",
        mimeType: "text/markdown",
      },
    ],
  })
);

// Dynamic resource with template
server.resource(
  "user-profile",
  new ResourceTemplate("users://{userId}/profile", {
    list: async () => ({
      resources: [
        { uri: "users://123/profile", name: "Alice" },
        { uri: "users://456/profile", name: "Bob" },
      ],
    }),
  }),
  async (uri, { userId }) => ({
    contents: [
      {
        uri: uri.href,
        text: JSON.stringify({ id: userId, name: "..." }),
        mimeType: "application/json",
      },
    ],
  })
);

server.prompt(
  "review-code",
  "Review code for best practices and potential issues",
  {
    language: z.string().describe("Programming language"),
    code: z.string().describe("The code to review"),
  },
  ({ language, code }) => ({
    messages: [
      {
        role: "user",
        content: {
          type: "text",
          text: [
            `Review the following ${language} code.`,
            `Focus on: correctness, performance, security, readability.`,
            `\n\n\`\`\`${language}\n${code}\n\`\`\``,
          ].join("\n"),
        },
      },
    ],
  })
);

server.tool(
  "query_database",
  "Execute a database query",
  { sql: z.string() },
  async ({ sql }) => {
    try {
      const result = await db.execute(sql);
      return {
        content: [{ type: "text", text: JSON.stringify(result) }],
      };
    } catch (error) {
      return {
        isError: true,
        content: [
          {
            type: "text",
            text: `Query failed: ${error instanceof Error ? error.message : "Unknown error"}`,
          },
        ],
      };
    }
  }
);