app = FastAPI(
    servers=[
        {"url": "/", "description": "Default, relative server"},
        {
            "url": "http://staging.localhost.tiangolo.com:8000",
            "description": "Staging but actually localhost still",
        },
        {"url": "https://prod.example.com"},
    ]
)


@app.get("/foo")
def foo():
    return {"message": "Hello World"}


client = TestClient(app)

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.

So, you might still need to use Pydantic models.

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## Opinions { #opinions }

"_[...] I'm using **FastAPI** a ton these days. [...] I'm actually planning to use it for all of my team's **ML services at Microsoft**. Some of them are getting integrated into the core **Windows** product and some **Office** products._"

<!-- /sponsors -->

<a href="https://fastapi.tiangolo.com/fastapi-people/#sponsors" class="external-link" target="_blank">Other sponsors</a>

## Opinions

"_[...] I'm using **FastAPI** a ton these days. [...] I'm actually planning to use it for all of my team's **ML services at Microsoft**. Some of them are getting integrated into the core **Windows** product and some **Office** products._"

                                    "converted": {
                                        "summary": "An example with converted data",
                                        "description": "FastAPI can convert price `strings` to actual `numbers` automatically",
                                        "value": {"name": "Bar", "price": "35.4"},
                                    },
                                    "invalid": {

    ),
    dirty: bool = False,
) -> None:
    """
    Serve with livereload a docs site for a specific language.

    This only shows the actual translated files, not the placeholders created with
    build-all.

    Takes an optional LANG argument with the name of the language to serve, by default
    en.
    """

## 0.125.0

### Breaking Changes

* 🔧 Drop support for Python 3.8. PR [#14563](https://github.com/fastapi/fastapi/pull/14563) by [@tiangolo](https://github.com/tiangolo).
    * This would actually not be a _breaking_ change as no code would really break. Any Python 3.8 installer would just refuse to install the latest version of FastAPI and would only install 0.124.4. Only marking it as a "breaking change" to make it visible.