The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

* Automatic data model documentation with <a href="https://json-schema.org/" class="external-link" target="_blank"><strong>JSON Schema</strong></a> (as...

There are several alternatives, including:

* <a href="https://www.uvicorn.org/" class="external-link" target="_blank">Uvicorn</a>: a high performance ASGI server.
* <a href="https://pgjones.gitlab.io/hypercorn/" class="external-link" target="_blank">Hypercorn</a>: an ASGI server compatible with HTTP/2 and Trio among other features.
* <a href="https://github.com/django/daphne" class="external-link" target="_blank">Daphne</a>: the ASGI server built for Django Channels.

## More info

To learn more about the options, check Starlette's documentation for:

* <a href="https://www.starlette.io/websockets/" class="external-link" target="_blank">The `WebSocket` class</a>.

And the rest will be handled by **FastAPI**.

If you run it and go to <a href="http://localhost:8000/v1/" class="external-link" target="_blank">http://localhost:8000/v1/</a> you will see the response from Flask:

```txt
Hello, World from Flask!
```

And if you go to <a href="http://localhost:8000/v2" class="external-link" target="_blank">http://localhost:8000/v2</a> you will see the response from FastAPI:

```JSON
{

  favicon: img/favicon.png
  language: en
repo_name: tiangolo/fastapi
repo_url: https://github.com/tiangolo/fastapi
edit_uri: ''
plugins:
  search: null
  macros:
    include_yaml:
    - external_links: ../en/data/external_links.yml
    - github_sponsors: ../en/data/github_sponsors.yml
    - people: ../en/data/people.yml
    - sponsors_badge: ../en/data/sponsors_badge.yml
    - sponsors: ../en/data/sponsors.yml
  redirects:

### Check the docs

Now you can start your app and go to <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

You will see your docs have the normal *path operations* and now also some **webhooks**:

For production you would use `fastapi run` instead. 🚀

Internally, **FastAPI CLI** uses <a href="https://www.uvicorn.org" class="external-link" target="_blank">Uvicorn</a>, a high-performance, production-ready, ASGI server. 😎

## `fastapi dev`

When you run `fastapi dev`, it will run on development mode.

import org.codehaus.plexus.testing.PlexusTest;
import org.eclipse.aether.DefaultRepositorySystemSession;
import org.eclipse.aether.internal.impl.DefaultChecksumPolicyProvider;
import org.eclipse.aether.internal.impl.DefaultRemoteRepositoryManager;
import org.eclipse.aether.internal.impl.DefaultUpdatePolicyAnalyzer;
import org.eclipse.aether.internal.impl.SimpleLocalRepositoryManagerFactory;
import org.eclipse.aether.repository.LocalRepository;

import org.eclipse.aether.internal.impl.scope.ManagedDependencyContextRefiner;
import org.eclipse.aether.internal.impl.scope.ManagedScopeDeriver;
import org.eclipse.aether.internal.impl.scope.ManagedScopeSelector;
import org.eclipse.aether.internal.impl.scope.OptionalDependencySelector;
import org.eclipse.aether.internal.impl.scope.ScopeDependencySelector;
import org.eclipse.aether.internal.impl.scope.ScopeManagerImpl;