To enable servers to push data to web pages over HTTP or using dedicated server-push protocols, this specification introduces the EventSource interface.

It uses the Server-Sent Events (SSE) web standard

You can get around this by forwarding your web server’s port on your router and then use your public IP address as the webhook URL but that’s super annoying, exposes your public IP address and it will very likely change because most home grade cable / DSL connections have dynamic IP addresses.Not only that, but some services require that you respond to webhooks over HTTPS, so now you would be responsible for setting up HTTPS too, when really all you want to do is test a webhook in development.

Webhooks are a really powerful concept. They let you integrate with third party services in a very easy way and you can do it without having to constantly pull information from a service.

Set the endpoint to Mailgun's Postbin. A Postbin is a web service that allows you to post data, which is then displayed through a browser. This allows you to quickly determine what is actually being transmitted to Mailgun's API.

PostBin, a simple web service for testing and logging of the receival of WebHooks (HTTP POST requests).