### About `root_path`

Keep in mind that the server (Uvicorn) won't use that `root_path` for anything else than passing it to the app.

But if you go with your browser to <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000/app</a> you will see the normal response:

```JSON
{

* 📝 Simplify example for docs for Additional Responses, remove unnecessary `else`. PR [#4693](https://github.com/tiangolo/fastapi/pull/4693) by [@adriangb](https://github.com/adriangb).

# OpenAPI Callbacks

You could create an API with a *path operation* that could trigger a request to an *external API* created by someone else (probably the same developer that would be *using* your API).