Got RESTful APIs? Great. API consumers love them. But today, such RESTful APIs are not enough for the evolving expectations of API consumers. Their apps need to be responsive, event-based and react to changes in near real-time.

This results in a new set of requirements for the APIs, which power the apps. APIs now need to provide concepts such as events, notifications, triggers, and subscriptions. These concepts are not natively supported by the REST architectural style.

Integration used to be all about APIs. Today it is about APIs and events. APIs allow for reading and writing data, calling functionality and starting processes. APIs connect us with actuators in the digital world that enable us to do and change things. We need support for events which allow for reacting to things happening in the environment. Events connect us with sensors in the digital world that wake us up, tell us that things have changed and what exactly has changed.

How do we realize events in an API context? In the new Webhooks Book, we study several approaches for realizing events and then focus in on webhooks. We study the concepts of webhooks and the overall architecture to make them work. We go into the detailed non-functional properties of a webhooks-based solution, such as security, reliability and developer experience. We show how to make webhooks work in a RESTful API portfolio with some detailed design proposals in OpenAPI.

New Requirements for APIs

Matthias Biehl

As API strategist, Matthias helps clients discover their opportunities for innovation with APIs & ecosystems and turn them into actionable digital strategies. Based on his experience in leading large-scale API initiatives in both business and technology roles, he shares best practices and provides both strategic and practical guidance. He has stayed a techie at heart and at some point, got a Ph.D. Matthias publishes a blog at, is the author of several books on APIs, and regularly speaks at technology conferences.