Tool Use and Function Calling

How Function Calling Works

Function calling is the mechanism that lets a model use tools. It is simpler than its reputation suggests.

The system hands the model a menu. Each tool's name, its description, and its parameter schema, all sitting in the context.

A schema is a spec of what inputs a tool accepts and what type each one is.

When the model decides it needs a tool, it does not run anything itself.

It emits a structured request instead, something like {"tool": "lookup_order", "args": {"order_id": "4711"}}.

Generation pauses there.