Intermediate · Generative AI

Function Calling

Visual diagram · (in preparation) · Math · (in preparation) · Worked example · 3 difficulty levels.

TL;DR. Provider-defined schemas that let an LLM invoke developer-supplied functions in a structured way.

Technical Definition

Provider-defined schemas that let an LLM invoke developer-supplied functions in a structured way.

How it works

Function calling is the API-level form of tool calling. The developer registers function signatures with descriptions; the model decides when to call them and with what arguments. It is the foundation of most production agents, plugins, and assistants.

Related Concepts

• Large Language Model (LLM) — A massive neural network trained on vast text corpora to understand and generate human language with remarkable fluency.
• AI Agent — An AI system that autonomously plans, uses tools, and takes actions to accomplish goals through iterative reasoning.
• Tool Calling — An LLM capability where the model emits structured calls to external functions or APIs.