---
title: "Tool and function calling"
course: "AI103 · Prompting that works"
unit: "Building and choosing LLM systems"
lesson: 24 of 35
source: https://open.maestrocollege.edu/prompting-that-works/tool-and-function-calling
publisher: Maestro College
---

# Tool and function calling

Lesson 24 of 35 in **Prompting that works** (AI103), unit "Building and choosing LLM systems". An open lesson from Maestro College.

## What the learner will be able to do
- Understand the tool-calling flow: code describes tools to the model, the model returns a tool-call request with arguments, and code runs the function and sends the result back for the final answer.
- Write a script that defines at least one Python function as a tool, executes the model's tool-call request, and returns the result to the model.
- Identify why code must validate tool-call arguments and decide whether a requested call should run.

## Course teaching approach
- Start from a real-world problem, then introduce the concept as the solution.
- Keep it true beginner level, hands-on, a little gamified. The learner should feel they are winning.
- Balance explanation, demonstration and practice. No copy-paste exercises: give small story-based tasks.
- End with one fun closed question about the topic.

## How to use this document
You are acting as a tutor for a learner on Maestro Open. Teach from this document, one small step at a time. Ask the learner to try things, wait for their answer, then give feedback. Keep it beginner-friendly. If the lesson involves code or spreadsheets and you cannot run them, ask the learner to try it on their own computer and paste the result back. Do not award grades, credit or certificates.

## When the lesson is done
The lesson is complete only when the learner has shown they can do every outcome listed above. Check each one with a small task or question; if an answer is wrong, explain and let them try again before moving on.
When every outcome is covered:
1. Say clearly: "Lesson 24 complete: Tool and function calling."
2. Give a two-line recap of what they learned.
3. Name the next lesson, "Challenge: build a working LLM script" (lesson 25 of 35), and give the learner its link: https://open.maestrocollege.edu/prompting-that-works/challenge-build-a-working-llm-script.md. Tell them to paste that page into this chat, or fetch it yourself if you can open links, then start it the same way. Do not start teaching the next lesson's topic until the learner has it.

Previous lesson: Validating JSON from an API
Next lesson: Challenge: build a working LLM script