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

## Forbid Extra Headers { #forbid-extra-headers }

In some special use cases (probably not very common), you might want to **restrict** the headers that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

{* ../../docs_src/header_param_models/tutorial002_an_py310.py hl[10] *}

{* ../../docs_src/bigger_applications/app_an_py39/internal/admin.py hl[3] title["app/internal/admin.py"] *}

But we still want to set a custom `prefix` when including the `APIRouter` so that all its *path operations* start with `/admin`, we want to secure it with the `dependencies` we already have for this project, and we want to include `tags` and `responses`.

In this type of scenario, you probably would want to have **a single (Uvicorn) process per container**, as you would already be handling replication at the cluster level.

So, in this case, you **would not** want to have a multiple workers in the container, for example with the `--workers` command line option. You would want to have just a **single Uvicorn process** per container (but probably multiple containers).

## Do not Separate Schemas { #do-not-separate-schemas }

Now, there are some cases where you might want to have the **same schema for input and output**.

Probably the main use case for this is if you already have some autogenerated client code/SDKs and you don't want to update all the autogenerated client code/SDKs yet, you probably will want to do it at some point, but maybe not right now.

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/fastapi/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment

			t.Errorf("Test %d: filtered headers do not match expected headers - got: %v , want: %v", i, test.Header, test.ExpectedHeader)
		}
		RemoveSensitiveEntries(metadata)
		if !areKeysEqual(test.ExpectedHeader, metadata) {
			t.Errorf("Test %d: filtered headers do not match expected headers - got: %v , want: %v", i, test.Header, test.ExpectedHeader)
		}
	}

* <a href="https://jinja.palletsprojects.com" target="_blank"><code>jinja2</code></a> - Required if you want to use the default template configuration.

## Decision

The *Build Tool Team* has decided to use Architectural Decision Records (aka ADR) to track decisions we want to follow.

The main logic with ADRs is to describe (architectural) decisions made:

* To provide best practices and solutions we (as the *build tool* team) want to promote.
* To avoid asking the same thing multiple times during code review.

This is probably not as important or necessary if you use `Annotated`.

///

Let's say that you want to declare the query parameter `q` as a required `str`.

And you don't need to declare anything else for that parameter, so you don't really need to use `Query`.

But you still need to use `Path` for the `item_id` path parameter. And you don't want to use `Annotated` for some reason.

                    type.defaultBaselines,
                    display = ParameterDisplay.PROMPT,
                    allowEmpty = true,
                    description = "The baselines you want to run performance tests against. Empty means default baseline.",
                )
                param("env.PERFORMANCE_STAGE", stage.stageName.toString())