Heroku app webhooks is now generally available. The offering enables developers to set auto-notifications for app changes of choice (e.g. domain setting changes, new releases, new add-ons, dyno formations, etc.). Such notifications are accomplished through HTTP POST requests; thus, anything that can receive a HTTP POST request is a candidate for Heroku app webhooks.
The Heroku team envisions app webhook adoption for internal communications use cases. Whether the communication is received via a dashboard, bot, or other method, app webhooks can greatly streamline such communications because the need for continuous polling of the Platform API vanishes. Webhooks are automatically delivered when changes occur.
Developers can easily integrate app webhooks into their app workflow using the webhooks CLI plugin. Developers simply subscribe the event of choice with a single command. When the event occurs (e.g. a new release, a domain setting change, etc.), Heroku sends a POST request to the applicable server endpoint. The POST request includes the specific details of the event. Check out the webhooks documentation to see specifics.
Heroku has published an app webhooks tutorial to help developers get started. Within the tutorial, users can launch a "webhook viewer" application to get a feel. The app allows developers to create a webhook and then check the contents of the webhook before integrating the webhook into a live application. Further, the viewer provides all HTTP request data, so debugging is simple.