FastAPI will use this return type to:

* **Validate** the returned data.
    * If the data is invalid (e.g. you are missing a field), it means that *your* app code is broken, not returning what it should, and it will return a server error instead of returning incorrect data. This way you and your clients can be certain that they will receive the data and the data shape expected.
* Add a **JSON Schema** for the response, in the OpenAPI *path operation*.

Vous devez vous assurer qu'il est unique pour chaque opération.

```Python hl_lines="6"

## The main `FastAPI`

Now, let's see the module at `app/main.py`.

Here's where you import and use the class `FastAPI`.

This will be the main file in your application that ties everything together.

And as most of your logic will now live in its own specific module, the main file will be quite simple.

### Import `FastAPI`

You import and create a `FastAPI` class as normally.

Be sure to check out the [public roadmap](https://blog.gradle.org/roadmap-announcement) for insight into what's planned for future releases.

## Upgrade instructions

Switch your build to use Gradle @version@ by updating your wrapper:

`./gradlew wrapper --gradle-version=@version@`

In the output, there's a line with something like:

```hl_lines="4"
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
```

That line shows the URL where your app is being served, in your local machine.

### Check it

Open your browser at <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000</a>.

You will see the JSON response as:

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

You must agree to the terms of [Developer Certificate of Origin](https://developercertificate.org/) by signing off your commits. We automatically verify that all commit messages contain a `Signed-off-by:` line with your email address. We can only accept PRs that have all commits signed off.

If you didn't sign off your commits before creating the pull request, you can fix that after the fact.

To sign off a single commit:

Be sure to check out the [public roadmap](https://blog.gradle.org/roadmap-announcement) for insight into what's planned for future releases.

## Upgrade instructions

Switch your build to use Gradle @version@ by updating your wrapper:

`./gradlew wrapper --gradle-version=@version@`

****

[[part5_begin]]
== Step 0. Before you Begin

1. You initialized your Java app in <<part1_gradle_init.adoc#part1_begin,part 1>>.
2. You ran several tasks in <<part2_gradle_tasks#part2_begin,part 2>>.
3. You learned about dependency management in <<part3_gradle_dep_man#part3_begin,part 3>>.
4. You applied a plugin to your app in <<part4_gradle_plugins#part4_begin,part 4>>.

== Step 1. Understanding Incremental Builds

You can view the latest and full list of accepted tags in [`doclint/HtmlTag.java`](https://docs.oracle.com/en/java/javase/11/docs/api/java.desktop/javax/swing/text/html/HTML.Tag.html) for your JDK of choice.

Attempt to limit your usage of HTML to: `"a", "h1", "h2", "h3", "h4", "em", "li", "ol", "p", "ul"`.

Some HTML element types allow authors to omit end tags: `<p>` and `<li>`.

### 1.1.3 Paragraphs

{!../../../docs_src/path_operation_advanced_configuration/tutorial005.py!}
```

If you open the automatic API docs, your extension will show up at the bottom of the specific *path operation*.

<img src="/img/tutorial/path-operation-advanced-configuration/image01.png">

And if you see the resulting OpenAPI (at `/openapi.json` in your API), you will see your extension as part of the specific *path operation* too:

```JSON hl_lines="22"
{