MCP (Model Context Protocol) is an open standard for connecting Claude to external data sources and tools. Instead of Claude only knowing what's in your codebase, it can call live APIs, read from databases, and interact with services.
An MCP server exposes tools that Claude calls like any other tool. The server handles the actual API call and returns results, so Claude never sees your credentials directly. I find this architecture matters more than it first appears, because it means you can rotate secrets without touching your prompts.
MCP uses stdio for local processes and streamable-http for web servers. SSE is deprecated in the official spec. You can connect to GitHub, Slack, Notion, Jira, Figma, Sentry, and many others.