Structured output is not the same as a real tool call
Separate “return JSON” from “actually did the thing.”
Two different things
- Structured output: the model formats intent as JSON, a table, or named fields
- Real tool use: the surrounding system uses those fields to fetch data or perform an action
Why the distinction matters
If the model only returns JSON, it did not actually:
- fetch the latest weather
- edit your repository
- book the room
It only described the next step clearly.
Why we still practice it
Structured output is where you learn to:
- identify the right tool
- extract required parameters
- leave a clean interface for later automation
That same skill carries into IDE agents and local agents.