MCP (Model Context Protocol) servers are how Claude Code reaches anything outside the repo - databases, APIs, internal services, file systems, you name it.

What it does

An MCP server exposes tools, resources, and prompts over a standard protocol. Claude Code connects to the server, loads the available capabilities, and makes them available as tools within the session. MCP is open and multi-vendor, so the same server works with different clients.

When to use it

Wiring up databases, issue trackers, dashboards, or internal APIs.
Exposing legacy systems to Claude Code without writing custom integrations.
Sharing integrations across the team via .mcp.json in the repo.
Building your own domain-specific tools that feel native.

Gotchas

MCP servers run with their own auth. Misconfig means you silently lose access.
Loaded MCP tools count against context and can slow tool selection. Use tool search for large suites.
Remote MCP servers introduce network dependency. Plan for offline or fallback behavior.

Official docs: https://code.claude.com/docs/en/mcp.md