I will show you some of the main concepts you should probably keep in mind when deploying a **FastAPI** application (although most of it applies to any other type of web application).

cookies and headers), and will put them in the final response that contains the value you returned, filtered by any `response_model`.

You can also declare the `Response` parameter in dependencies, and set the status code in them. But keep in mind that the last one to be set will win....

So, you can declare your function as:

{* ../../docs_src/path_params_numeric_validations/tutorial002_py39.py hl[7] *}

But keep in mind that if you use `Annotated`, you won't have this problem, it won't matter as you're not using the function parameter default values for `Query()` or `Path()`.

{* ../../docs_src/path_params_numeric_validations/tutorial002_an_py39.py *}

Then set Cookies in it, and then return it:

{* ../../docs_src/response_cookies/tutorial001_py39.py hl[10:12] *}

/// tip

Keep in mind that if you return a response directly instead of using the `Response` parameter, FastAPI will return it directly.

### `Query` as the default value or in `Annotated` { #query-as-the-default-value-or-in-annotated }

Keep in mind that when using `Query` inside of `Annotated` you cannot use the `default` parameter for `Query`.

Instead, use the actual default value of the function parameter. Otherwise, it would be inconsistent.

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>.

## 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.

* 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>.

 * [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.

* 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.