Definition
Function calling is a specific implementation of tool use where the AI model generates structured JSON output that maps to predefined function signatures. The model selects which function to call and provides the required parameters in a structured format, which the application then executes.
Example
The model outputs {"function": "send_email", "parameters": {"to": "[email protected]", "subject": "Q2 Report", "body": "..."}} which the application parses and executes.
Why it matters
Function calling is the mechanism that turns AI reasoning into real-world actions. It's the bridge between "thinking" and "doing."