Glossary · 5 · Building with AI: APIs, tools and agents

Tool use (function calling)

Also known as: Function calling, Tool calling

Tool use, also called function calling, is the ability of a language model to request that the application run a defined function — such as a search, a database query or an API call — by returning a structured call with arguments, and then to use the result in its answer.

Expert
Developers

In one sentence

Tool use and function calling explained: how language models call search, databases and APIs — the building block of AI agents.

Example

Asked “Is spare part 4711 in stock?”, the model returns a call to check_stock(part="4711"); the application runs it and the model phrases the answer from the result.

Why it matters on your learning path

Technical project managers: Every tool an AI can call is a permission. Decide deliberately which actions need human approval.
Developers: Describe tools with precise names, descriptions and JSON schemas; validate arguments and never let the model execute unchecked actions.