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Tool use and function calling

**Tool use** lets a model call external functions—search, calculators, calendars, databases—instead of only emitting prose. **Function calling** is a common API pattern: the model returns a structured “please call this tool with these ar...

What it is

Tool use lets a model call external functions—search, calculators, calendars, databases—instead of only emitting prose. Function calling is a common API pattern: the model returns a structured “please call this tool with these arguments” message.

Why it matters

Tools ground some answers and enable agents. They also expand blast radius if permissions are too wide (Course 29).

How it works (plain)

  1. Developer registers tools with names, descriptions, argument schemas
  2. Model chooses a tool when needed
  3. App runs the tool safely
  4. Result returns to the model
  5. Model continues

Humans should approve high-risk tools (money movement, deletes, public posts).

Everyday example

“What’s 17.5% tip on $86.40?” → calculator tool beats mental arithmetic tokenization quirks.

Try it

List three tools you would allow an email agent—and three you would never allow without a human click.

Myths

⚠️ Myth: Tools make models truthful.
✓ Reality: Bad queries or bad retrieved results still mislead.
⚠️ Myth: More tools equal a better agent.
✓ Reality: Least privilege beats a junk drawer of APIs.

Sources