MCP, the Model Context Protocol, is an open standard that lets AI agents talk to external tools and data sources through small programs called MCP servers. Instead of each agent inventing its own integration format, an agent that "speaks MCP" can connect to any MCP server — for filesystem access, GitHub, a browser, documentation, and more — using one common protocol.In practice, you add MCP servers to a coding agent like Claude Code, Cursor or Cline, and the agent gains those servers' tools. Each server advertises its tools through a manifest the agent loads.
Why MCP matters in 2026
MCP matters because it's become the de-facto way to extend coding agents — but it has a token cost worth understanding. The tool definitions from every connected server are sent to the model as part of the context, and re-sent on each turn, so adding many servers quietly inflates token usage whether or not you use those tools. The fix is loading tools lazily and pruning servers you don't use; see Best MCP servers for Claude Code.
When MCP isn't the right tool
For tools you rarely call — a server you almost never use still taxes every turn; remove it.
For simple local actions — sometimes a direct command is cheaper than routing through a tool manifest.