by Amit Shekhar · 13 June 2026
How does Function Calling work in LLMs?
How Function Calling works in LLMs. We will see what it is, why we need it, the key insight behind it, and how it powers AI agents and assistants step by step.
Read on Outcome School ↗then come back to lock it in
Before you read, guessWhy is function calling necessary for large language models?
Ten seconds, a guess, then read — a wrong guess still makes the answer stick.
What this article covers
- What is Function Calling
- Why We Need Function Calling
- The Key Insight: The Model Does Not Run the Function
- How Function Calling Works Step by Step
- A Concrete Example: get_weather(city)
- The Conversation Loop
- Multi-Step and Parallel Function Calling
- Relation to Structured Outputs and JSON Mode
- Real-World Use: The Backbone of AI Agents
The article lives on outcomeschool.com. Read it there, then come back: the tutor in the margin has read it and will answer questions, and the questions below check what stayed.