MCP Servers

What is MCP?

The Model Context Protocol (MCP) is an open standard that lets AI tools connect to external data sources and services. Think of MCP servers as plugins that extend Claude Code's capabilities beyond reading and writing local files.

With MCP, Claude Code can query databases, interact with GitHub, access documentation, and communicate with any API — all securely and with your explicit configuration.

How MCP Works

• MCP Server — A lightweight process that exposes tools and resources to the AI agent
• MCP Client — Claude Code itself, which connects to configured servers
• Tools — Actions the server exposes (e.g., "query database", "create GitHub issue")
• Resources — Data the server can provide (e.g., database schemas, API documentation)

Configuring MCP Servers

MCP servers are configured in your project's .claude/ directory or globally:

Project-Level Configuration

Use the Claude Code CLI to add MCP servers:

# Add a GitHub MCP server
claude mcp add github-server -e GITHUB_TOKEN=ghp_your_token -- npx -y @modelcontextprotocol/server-github

# Add a PostgreSQL MCP server
claude mcp add postgres-server -e DATABASE_URL=postgresql://user:pass@localhost/mydb -- npx -y @modelcontextprotocol/server-postgres

# Add a filesystem MCP server for docs
claude mcp add docs-server -- npx -y @modelcontextprotocol/server-filesystem /path/to/docs

Project-Level Config File

You can also manually edit .claude/mcp.json:

{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_TOKEN": "ghp_your_token_here"
      }
    },
    "postgres": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-postgres"],
      "env": {
        "DATABASE_URL": "postgresql://user:pass@localhost:5432/mydb"
      }
    }
  }
}

Popular MCP Servers

Server	What It Does	Package
GitHub	Read PRs, issues, repo files	@modelcontextprotocol/server-github
PostgreSQL	Query databases, read schemas	@modelcontextprotocol/server-postgres
Filesystem	Access files outside your project	@modelcontextprotocol/server-filesystem
Puppeteer	Browser automation	@modelcontextprotocol/server-puppeteer

Managing MCP Servers

# List all configured servers
claude mcp list

# Remove a server
claude mcp remove github-server

# Check server status
claude mcp list

Security Best Practices

• Use read-only database credentials — Prevent accidental data modifications
• Scope GitHub tokens — Only grant the permissions Claude actually needs
• Don't commit secrets — Add .claude/mcp.json to .gitignore if it contains tokens
• Use environment variables — Reference $ENV_VAR instead of hardcoding credentials

What's Next

In the next episode, we'll learn about Subagents — how Claude Code can spawn child agents to handle complex multi-step tasks concurrently.