On voit bien dans la documentation que `item_id` est déclaré comme entier.

## Les avantages d'avoir une documentation basée sur une norme, et la documentation alternative.

    * FastAPI provides more features on top of Starlette. Features that you almost always need when building APIs, like data validation and serialization. And by using it, you get automatic documentation for free (the automatic documentation doesn't even add overhead to running applications, it is generated on startup).

It was one of the first examples of **automatic API documentation**, and this was specifically one of the first ideas that inspired "the search for" **FastAPI**.

!!! note
    Django REST Framework was created by Tom Christie. The same creator of Starlette and Uvicorn, on which **FastAPI** is based.


!!! check "Inspired **FastAPI** to"
    Have an automatic API documentation web user interface.

    This is incredibly helpful while developing and debugging code that interacts with your API.

## Documentation

And when you open your browser at <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>, you will see an automatic, interactive, API documentation like:

<img src="/img/tutorial/path-params/image01.png">

!!! check

And of course, it supports the same:

* data validation
* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

!!! info
    Keep in mind that dataclasses can't do everything Pydantic models can do.

FastAPI will use this `response_model` to do all the data documentation, validation, etc. and also to **convert and filter the output data** to its type declaration.

!!! tip
    If you have strict type checks in your editor, mypy, etc, you can declare the function return type as `Any`.

    That way you tell the editor that you are intentionally returning anything. But FastAPI will still do the data documentation, validation, filtering, etc. with the `response_model`.

Vous pouvez déclarer des réponses supplémentaires, avec des codes HTTP, des types de médias, des descriptions, etc.

Ces réponses supplémentaires seront incluses dans le schéma OpenAPI, elles apparaîtront donc également dans la documentation de l'API.

Mais pour ces réponses supplémentaires, vous devez vous assurer de renvoyer directement une `Response` comme `JSONResponse`, avec votre code HTTP et votre contenu.

## Réponse supplémentaire avec `model`

{"message": "Hello World"}
```

### Interactive API docs

Now go to <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

You will see the automatic interactive API documentation (provided by <a href="https://github.com/swagger-api/swagger-ui" class="external-link" target="_blank">Swagger UI</a>):

![Swagger UI](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png)

* `externalDocs`: a `dict` describing external documentation with:
    * `description`: a `str` with a short description for the external docs.
    * `url` (**required**): a `str` with the URL for the external documentation.

### Create metadata for tags

Let's try that in an example with tags for `users` and `items`.

    * 👆 💪 ⚒ 🚮 📛 ⏮️ 🔢 `docs_url`.
    * 👆 💪 ❎ ⚫️ ⚒ `docs_url=None`.
* **📄**: 🍦 `/redoc`.
    * 👆 💪 ⚒ 🚮 📛 ⏮️ 🔢 `redoc_url`.
    * 👆 💪 ❎ ⚫️ ⚒ `redoc_url=None`.

🖼, ⚒ 🦁 🎚 🍦 `/documentation` & ❎ 📄:

```Python hl_lines="3"
{!../../../docs_src/metadata/tutorial003.py!}