Learn AI · Level 3 · Tech and tools · step 9 of 16 · word 3 of 6
What is function calling (tool use) in AI?
Function calling, or tool use, lets an AI model ask an app to do something for it, such as check the weather, search a database or send an email, and then use the result.
In plain English
On its own, a model can only write text. With function calling, the app tells the model which tools exist, such as “get_weather(city)”. When a question needs one, the model replies with a request to use it. The app runs the tool and hands back the result, and the model writes the answer.
The model never runs anything itself: the app decides what actually happens. Every major model supports this now, and it is what makes AI agents possible.
An example
You ask: “Do I need an umbrella in Mumbai today?” The model asks for get_weather(“Mumbai”), gets back “80% chance of rain”, and says yes, take one.
Watch out
Every tool is a new power. Give a model only the tools it needs, and ask a person to confirm anything that spends money or sends messages. MCP is a standard way to offer tools to many apps.
Learn AI path · Level 3 · Tech and tools · step 9 of 16
Next wordMCP (Model Context Protocol) →See all of level 3