WebSub (formerly PubSubHubbub) is an open protocol for distributed publish–subscribe communication on the Internet.[1] Initially designed to extend the Atom (and RSS) protocols for data feeds, the protocol can be applied to any data type (e.g. HTML, text, pictures, audio, video) as long as it is accessible via HTTP. Its main purpose is to provide real-time notifications of changes, which improves upon the typical situation where a client periodically polls the feed server at some arbitrary interval. In this way, WebSub provides pushed HTTP notifications without requiring clients to spend resources on polling for changes.
In October 2017, PubSubHubbub was renamed to WebSub for simplicity and clarity.[2] As of January 2018[update], the WebSub protocol has been adopted by the W3C as a Recommendation.[3]