</div>

    !!! tip
        By adding the `standard`, Uvicorn will install and use some recommended extra dependencies.

        That including `uvloop`, the high-performance drop-in replacement for `asyncio`, that provides the big concurrency performance boost.

        When you install FastAPI with something like `pip install fastapi` you already get `uvicorn[standard]` as well.

=== "Hypercorn"

When you install FastAPI (e.g. with `pip install fastapi`), it includes a package called `fastapi-cli`, this package provides the `fastapi` command in the terminal.

To run your FastAPI app for development, you can use the `fastapi dev` command:

<div class="termy">

```console

```Python hl_lines="1  46-47"
{!../../../docs_src/websockets/tutorial001.py!}
```

!!! note "Technical Details"
    You could also use `from starlette.websockets import WebSocket`.

    **FastAPI** provides the same `WebSocket` directly just as a convenience for you, the developer. But it comes directly from Starlette.

## Await for messages and send messages

In your WebSocket route you can `await` for messages and send messages.

* Collect the money.
* Send a notification back to the API user (the external developer).
    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").

## The normal **FastAPI** app

Let's first see how the normal API app would look like before adding the callback.

      format: !!python/name:pymdownx.superfences.fence_code_format ''
  pymdownx.tabbed:
    alternate_style: true
  pymdownx.tilde: null
  attr_list: null
  md_in_html: null
extra:
  analytics:
    provider: google
    property: G-YNEVN69SC3
  social:
  - icon: fontawesome/brands/github-alt
    link: https://github.com/tiangolo/fastapi
  - icon: fontawesome/brands/discord
    link: https://discord.gg/VQjSZaeJmf

### Dependency Injection

FastAPI includes an extremely easy to use, but extremely powerful <abbr title='also known as "components", "resources", "services", "providers"'><strong>Dependency Injection</strong></abbr> system.

* Even dependencies can have dependencies, creating a hierarchy or **"graph" of dependencies**.
* All **automatically handled** by the framework.