Tool Use and Function Calling

1. The Mechanics, Demystified

Function calling is the mechanism that lets a model use tools, and 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 right there in the context. A schema is just 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