OpenAI Function Calling
OpenAI
The definitive reference for implementing tool use in OpenAI-powered agents, written and maintained by the creators of the API itself.
September 13, 2026
Developers building tool-calling agents with GPT models
About
OpenAI's authoritative documentation on function calling, a core capability for building AI agents that interact with external tools and APIs. Covers how to define function schemas, handle function calls in the API response, and implement agent loops that execute functions based on model decisions. Essential reference for anyone building agents on the OpenAI platform.
Who is it for
Engineers and prompt engineers building production agents with OpenAI models. Developers who need to connect LLMs to external tools, APIs, and data sources for autonomous decision-making.
OpenAI Function Calling Guide
This is the canonical reference directly from OpenAI, covering the exact mechanism that powers tool use in GPT-4 and GPT-3.5 agents. It includes practical examples, best practices, and implementation patterns essential for production agentic systems.
What you learn
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