These features are what Marshmallow was built to provide. It is a great library, and I have used it a lot before.

But it was created before there existed Python type hints. So, to define every <abbr title="the definition of how data should be formed">schema</abbr> you need to use specific utils and classes provided by Marshmallow.

!!! check "Inspired **FastAPI** to"
    Use code to define "schemas" that provide data types and validation, automatically.

{!../../../docs_src/custom_docs_ui/tutorial001.py!}
```

!!! tip
    The *path operation* for `swagger_ui_redirect` is a helper for when you use OAuth2.

    If you integrate your API with an OAuth2 provider, you will be able to authenticate and come back to the API docs with the acquired credentials. And interact with it using the real OAuth2 authentication.

In most cases you would (and should) have a "termination proxy" handling HTTPS for you on top, this will depend on how you deploy your application, your provider might do this for you, or you might need to set it up yourself.

!!! tip

Specifically, to see Uvicorn, Starlette and FastAPI compared together (among many other tools).

The simpler the problem solved by the tool, the better performance it will get. And most of the benchmarks don't test the additional features provided by the tool.

The hierarchy is like:

* **Uvicorn**: an ASGI server
    * **Starlette**: (uses Uvicorn) a web microframework

The most common is the implicit flow.

The most secure is the code flow, but is more complex to implement as it requires more steps. As it is more complex, many providers end up suggesting the implicit flow.

!!! note

```

### 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)

### Alternative API docs

      "url": "https://errors.pydantic.dev/2.1/v/int_parsing"
    }
  ]
}
```

because the path parameter `item_id` had a value of `"foo"`, which is not an `int`.

The same error would appear if you provided a `float` instead of an `int`, as in: <a href="http://127.0.0.1:8000/items/4.2" class="external-link" target="_blank">http://127.0.0.1:8000/items/4.2</a>

!!! check

                """
            ),
        ] = None,
        auto_error: Annotated[
            bool,
            Doc(
                """
                By default, if the HTTP Basic authentication is not provided (a
                header), `HTTPBasic` will automatically cancel the request and send the
                client an error.

                If `auto_error` is set to `False`, when the HTTP Basic authentication

# Generate Clients

As **FastAPI** is based on the OpenAPI specification, you get automatic compatibility with many tools, including the automatic API docs (provided by Swagger UI).

One particular advantage that is not necessarily obvious is that you can **generate clients** (sometimes called <abbr title="Software Development Kits">**SDKs**</abbr> ) for your API, for many different **programming languages**.

## OpenAPI Client Generators

                """
            ),
        ] = None,
        auto_error: Annotated[
            bool,
            Doc(
                """
                By default, if no HTTP Authorization header is provided, required for
                OAuth2 authentication, it will automatically cancel the request and
                send the client an error.