And as the `Response` can be used frequently to set headers and cookies, **FastAPI** also provides it at `fastapi.Response`.

///

## Custom Headers { #custom-headers }

Keep in mind that custom proprietary headers can be added <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">using the `X-` prefix</a>.

{* ../../docs_src/header_param_models/tutorial003_an_py310.py hl[19] *}

/// warning

Before setting `convert_underscores` to `False`, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.

///

## Summary { #summary }

## Check the Docs { #check-the-docs }

You can see the defined cookies in the docs UI at `/docs`:

<div class="screenshot">
<img src="/img/tutorial/cookie-param-models/image01.png">
</div>

/// info

Have in mind that, as **browsers handle cookies** in special ways and behind the scenes, they **don't** easily allow **JavaScript** to touch them.

 * [Coil](https://github.com/coil-kt/coil): An image loading library for Android backed by Kotlin Coroutines.
 * [Communicator](https://github.com/Taig/Communicator): An OkHttp wrapper for Scala built with Android in mind.
 * [Cronet Transport for OkHttp](https://github.com/google/cronet-transport-for-okhttp): A HTTP3 ready transport layer for OkHttp on Android, based on Chromium network stack.

But when checking benchmarks and comparisons you should keep the following in mind.

## Benchmarks and speed { #benchmarks-and-speed }

When you check the benchmarks, it is common to see several tools of different types compared as equivalent.

* You can then further modify the `response` before returning it.

{* ../../docs_src/middleware/tutorial001_py39.py hl[8:9,11,14] *}

/// tip

Keep in mind that custom proprietary headers can be added <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">using the `X-` prefix</a>.

## Code size { #code-size }

This example might seem verbose. Keep in mind that we are mixing security, data models, utility functions and *path operations* in the same file.

But here's the key point.

The security and dependency injection stuff is written once.

* If you are feeling too generous, you can try to **create an example** like that yourself, just based on the description of the problem. Just keep in mind that this might take a lot of time and it might be better to ask them to clarify the problem first.

### Suggest solutions { #suggest-solutions }

* 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.

There is some assistance in the IDE for this plus a lot of validation that is applied at build time and on CI, but it is useful to keep these constraints in mind as well.

See [Gradle runtimes](runtimes.md) for a list of these runtimes and more details.

### Build execution model