Using MCP Servers in Claude Code

What is MCP?

The Model Context Protocol (MCP) is a standard interface that lets Claude Code communicate with external tools and data sources. Think of it like USB for AI — any tool that implements the protocol can plug into Claude Code.

Why MCP Matters

Out of the box, Claude Code can read files and run commands. MCP extends that to:

• Databases — Query your dev database, inspect schemas, run migrations
• APIs — Hit internal services, check deployment status, read documentation
• Custom tools — Anything you can write a function for

Setting Up Your First MCP Server

Create a .mcp.json file in your project root:

{
  "mcpServers": {
    "weather": {
      "command": "node",
      "args": ["./mcp-servers/weather/dist/index.js"]
    }
  }
}

Building a Simple MCP Server

Here's a minimal MCP server in TypeScript:

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

const server = new McpServer({
  name: "my-tools",
  version: "1.0.0",
});

server.tool(
  "lookup_user",
  "Look up a user by email",
  { email: z.string().email() },
  async ({ email }) => ({
    content: [{
      type: "text" as const,
      text: JSON.stringify({ id: "123", email, name: "Jane" }),
    }],
  })
);

const transport = new StdioServerTransport();
server.connect(transport);

How Claude Discovers Tools

When you start a session, Claude Code reads your .mcp.json, starts each server, and discovers what tools are available. When you ask a question that needs external data, Claude automatically calls the right tool.

Best Practices

1. One tool per task — Don't create a do_everything tool. Keep them focused.
2. Validate inputs with Zod — Always validate what Claude sends.
3. Return structured JSON — Easier for Claude to parse than prose.
4. Handle errors gracefully — Return helpful messages so Claude can retry or self-correct.

Popular MCP Servers

The ecosystem is growing fast. Some useful ones:

• @modelcontextprotocol/server-filesystem — Enhanced file operations
• @modelcontextprotocol/server-github — GitHub API access
• @modelcontextprotocol/server-postgres — PostgreSQL queries
• Community servers for Slack, Linear, Notion, and more