```Python hl_lines="8  10-11"
{!> ../../../docs_src/response_model/tutorial003_02.py!}
```

This simple case is handled automatically by FastAPI because the return type annotation is the class (or a subclass) of `Response`.

And tools will also be happy because both `RedirectResponse` and `JSONResponse` are subclasses of `Response`, so the type annotation is correct.

### Annotate a Response Subclass

## Standards-based benefits, alternative documentation

And because the generated schema is from the <a href="https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.1.0.md" class="external-link" target="_blank">OpenAPI</a> standard, there are many compatible tools.

ItemsService.createItemItemsPost({name: "Plumbus", price: 5})
```

...that's because the client generator uses the OpenAPI internal **operation ID** for each *path operation*.

OpenAPI requires that each operation ID is unique across all the *path operations*, so FastAPI uses the **function name**, the **path**, and the **HTTP method/operation** to generate that operation ID, because that way it can make sure that the operation IDs are unique.

So, the frontend (that runs in the browser) would try to reach `/openapi.json` and wouldn't be able to get the OpenAPI schema.

Because we have a proxy with a path prefix of `/api/v1` for our app, the frontend needs to fetch the OpenAPI schema at `/api/v1/openapi.json`.

```mermaid
graph LR

browser("Browser")

            """
            An alternative name for the parameter field.

            This will be used to extract the data and for the generated OpenAPI.
            It is particularly useful when you can't use the name you want because it
            is a Python reserved keyword or similar.
            """
        ),
    ] = None,
    alias_priority: Annotated[
        Union[int, None],
        Doc(
            """

<img src="/img/tutorial/sub-applications/image02.png">

If you try interacting with any of the two user interfaces, they will work correctly, because the browser will be able to talk to each specific app or sub-app.

### Technical Details: `root_path`

## Run it

!!! info
    First install <a href="https://github.com/Kludex/python-multipart" class="external-link" target="_blank">`python-multipart`</a>.

    E.g. `pip install python-multipart`.

    This is because **OAuth2** uses "form data" for sending the `username` and `password`.

Run the example with:

<div class="termy">

```console
$ uvicorn main:app --reload

``` hl_lines="5"
.
├── app
│   ├── __init__.py
│   ├── main.py
│   └── test_main.py
```

Because this file is in the same package, you can use relative imports to import the object `app` from the `main` module (`main.py`):

```Python hl_lines="3"
{!../../../docs_src/app_testing/test_main.py!}
```

But if your connection to the server is lost, the **running process** will probably die.

And if the server is restarted (for example after updates, or migrations from the cloud provider) you probably **won't notice it**. And because of that, you won't even know that you have to restart the process manually. So, your API will just stay dead. 😱

### Run Automatically on Startup

### Add some custom `tags`, `responses`, and `dependencies`

We are not adding the prefix `/items` nor the `tags=["items"]` to each *path operation* because we added them to the `APIRouter`.

But we can still add _more_ `tags` that will be applied to a specific *path operation*, and also some extra `responses` specific to that *path operation*: