How do AI agents call tools and APIs?
The model is given tool definitions (a name, a description and an input schema) alongside the conversation. When it decides a tool is needed it returns a structured call instead of text; the toolbox node executes the call, records the result and hands it back to the model for the next turn. The loop repeats until the model answers or the iteration limit is reached.
The description is written for the model: what the tool does, what it needs, what it returns and when to use it. A good description is most of the difference between an agent that uses a tool at the right moment and one that guesses.