Design Principles

To compare the interface design approaches of SOAP-based web services to those of REST services, the former tend to be centered around operations that are usually use-case specific and reveal service implementation details (inside-out perspective). This leads to closely coupled systems which tend to get brittle and fragile as complexity grows. In contrast, REST is all about (business) entities found in the system and exposed as resource endpoints — leading to interfaces which abstract away implementation details (outside-in perspective) and are thereby more broadly usable and longer lasting. .

API Design Principles

  1. We prefer REST-based APIs
  2. We prefer systems to be truly RESTful
  3. We strive to build interoperating distributed systems that different teams can evolve in parallel

An important principle for (RESTful) API design and usage is Postel’s Law, aka the Robustness Principle (RFC 1122):

“Be liberal in what you accept, be conservative in what you send.”

The ability to extend service definitions after the initial release without affecting already deployed clients is key to preserve agility and evolvability of those services. For a more in-depth discussion regarding its applicability on API Design, please read the Message Schema and Postel’s Law chapter.

Read the following to gain additional insight on the RESTful service architecture paradigm and general RESTful API design style:

We apply the RESTful web service principles to all kind of application components, whether they provide functionality via the Internet or via the intranet as larger application elements. We strive to build interoperating distributed systems that different teams can evolve in parallel.


This chapter was adopted from the Zalando API Styleguide