A webhook in web development is a method of augmenting or altering the behaviour of a web page, or web application, with custom callbacks. These callbacks may be maintained, modified, and managed by third-party users and developers who may not necessarily be affiliated with the originating website or application. The term "webhook" was coined by Jeff Lindsay in 2007 from the computer programming term hook.
Webhooks are "user-defined HTTP callbacks". They are usually triggered by some event, such as pushing code to a repository or a comment being posted to a blog. When that event occurs, the source site makes an HTTP request to the URL configured for the webhook. Users can configure them to cause events on one site to invoke behaviour on another. The action taken may be anything. Common uses are to trigger builds with continuous integration systems or to notify bug tracking systems. Since they use HTTP, they can be integrated into web services without adding new infrastructure. However, there are also ways to build a message queueing service on top of HTTP—some RESTful examples include IronMQ and RestMS.