Function calling lets the model decide when to call your functions and with what arguments — the foundation of AI agents.

How It Works

1. Define functions with name, description, and parameter schema
2. Pass them to the API in the tools parameter
3. Model returns a tool_calls object when it wants to call a function
4. Your code executes the function
5. Return the result to the model to continue

Example Tool Definition

tools = [{
    "type": "function",
    "function": {
        "name": "get_weather",
        "description": "Get current weather for a city",
        "parameters": {
            "type": "object",
            "properties": {
                "city": {"type": "string"}
            },
            "required": ["city"]
        }
    }
}]

Reference:

Function calling documentation

https://en.wikipedia.org/wiki/Special:Search?search=Function%20Calling