Most applications and popular websites provide a REST application programming interface (API) these days. Amazon, Netflix, Twillio, and thousands of companies have a public-facing interface that has become a significant part of their business growth.
A RESTful API is a web service API that adheres to the REST architectural properties. We briefly alluded to Roy Fielding's thesis in Chapter 4, Views and URLs, which introduced the REST architectural style. Due to its simplicity and flexibility for a variety of use cases such as mobile applications, it has become a de facto standard in the industry for programmatic interfaces.
There are six architectural constraints of a pure RESTful system, and these are, as follows: