* This allows declaring a parameter like `user_id: str = None` that can be taken from a query parameter, but the same *path operation* can be included in a router with a path `/users/{user_id}`, in which case will be taken from the path and will be required.
    * PR [#464](https://github.com/tiangolo/fastapi/pull/464) by [@jonathanunderwood](https://github.com/jonathanunderwood).

<font color="#4E9A06">INFO</font>:     Application startup complete.
```

</div>

That command line program called `fastapi` is **FastAPI CLI**.

FastAPI CLI takes the path to your Python program and automatically detects the variable with the FastAPI (commonly named `app`) and how to import it, and then serves it.

For production you would use `fastapi run` instead. 🚀