Vibe CodingTool Use (Function Calling)
The mechanism that lets a model call external functions — read a file, run a command, query an API — instead of only producing text.
On its own, a language model just predicts text. Tool use (also called function calling) is the layer that lets it take real actions: the model is given a list of available functions with descriptions of what they do, and when it decides one is needed, it outputs a structured request to call it — the surrounding system executes the function and feeds the result back in.
This is the mechanical foundation underneath every AI coding agent’s ability to read files, edit code, or run a test suite. Model Context Protocol is one standardized way of exposing tools to a model; tool use is the more general capability that makes it possible.
Why it matters
Knowing exactly which tools an agent has been given tells you the real blast radius of what it can do to your system — not just what it can say.