Tools — when AI takes action

You decided when chat is enough and when to call Weather, Calendar, Calculator, or none. That’s the heart of function calling.

1. Model reads the user ask
2. It picks a tool + arguments (or none)
3. Your app runs the tool safely
4. The result goes back so the model can answer with real data

LLMs are brains for language. Tools are hands for actions and live facts.

• “What’s the weather in Lisbon?” → weather API
• “Add lunch tomorrow at 1” → calendar
• “What’s 18% tip on 64?” → calculator (don’t make the model invent math)

Never let a model invent tool results. If the tool didn’t run, say so. Also keep auth and permissions in your code, not in freeform chat.

Write two user messages: one that needs a tool, one that only needs knowledge. Label which is which.