This page helps developers to redirect a callback URL to localhost. You first need to enable the redirecting. After that it will redirect to your localhost development environment in 5 seconds.
You can use tolocalhost.com/[:port] to redirect to a specific port.
As a web developer you sometimes just want to be able to quickly test an integration with an OAuth service provider. The problem is that these redirect you back to a callback URL which often can not be localhost. With this domain you're able to redrect the callback to: tolocalhost.com and end up on your development application on localhost.