MCP didn't invent a new way for models to use tools — it standardized how tools get exposed to them, so one server can serve many different clients instead of being rebuilt per app.
Every modern LLM API already supports native tool calling (also called function calling): you describe a function's name, arguments, and purpose in a schema, hand that schema to the model alongside a prompt, and the model can emit a structured request to call it. The Model Context Protocol (MCP)doesn't replace that mechanism — it standardizes what sits around it: a common client-server protocol so that any MCP-compatible client (an IDE, a desktop app, an agent framework) can discover and call the tools exposed by any MCP server, without that server having to be hand-wired into every single app's proprietary function-calling format.