Function Calling / Tool Use
The ability of an AI model to call external tools or APIs — like a calculator, search engine, or database — instead of just generating text.
01 Definition
Function calling (also called tool use) lets an AI model recognize when a task needs an outside capability it doesn't have natively — like real-time data, precise math, or executing code — and call a defined function or tool to get that result, then incorporate it into its answer.
02 Why It Matters
This is the technical foundation behind AI agents and most 'AI that can actually do things' — without it, a model can only generate text based on what it already knows.
03 Example
An AI assistant calling a weather API when you ask 'what's the weather today?' instead of guessing.