Claude Code MCP Servers

What is MCP?

MCP (Model Context Protocol) is an open standard from Anthropic that lets Claude Code call external tools and access real data sources. Instead of pasting content into prompts, Claude can directly query your database, read GitHub PRs, search the web, or control a browser — in real-time, during your conversation.

Each MCP server is a local process that exposes a set of tools. Claude Code starts them automatically when you open a session and can call their tools the same way it calls built-in tools like Read or Bash.

How to Add an MCP Server

The fastest way is the CLI:

# Add a server globally (available in all projects)
claude mcp add github -- npx -y @modelcontextprotocol/server-github

# Add a server per-project (committed to .claude/settings.json)
claude mcp add postgres -- npx -y @modelcontextprotocol/server-postgres postgresql://localhost/mydb

Or edit .claude/settings.json directly:

{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": { "GITHUB_TOKEN": "ghp_yourtoken" }
    },
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/home/you/projects"]
    }
  }
}

Official MCP Servers (Anthropic)

Community MCP Servers

Securing MCP Servers

MCP servers run with the same permissions as your shell. Follow these practices:

• Use permissions in settings.json to require human approval for destructive MCP tool calls.
• Add a PreToolUse hook that inspects CLAUDE_TOOL_NAME and exits 1 to block any call you didn't expect.
• Pass credentials via env in the server config — never hardcode tokens in args.
• Use read-only database users where writes aren't needed (e.g. Postgres GRANT SELECT only).

Building a Custom MCP Server

Any process that speaks MCP JSON-RPC over stdio is a valid server. Minimal TypeScript example:

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";

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

server.setRequestHandler("tools/list", async () => ({
  tools: [{ name: "hello", description: "Say hello", inputSchema: {
    type: "object", properties: { name: { type: "string" } }, required: ["name"]
  }}]
}));

server.setRequestHandler("tools/call", async (req) => ({
  content: [{ type: "text", text: `Hello, ${req.params.arguments.name}!` }]
}));

await server.connect(new StdioServerTransport());

Register it: claude mcp add hello -- node /path/to/server.js

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