What is a REST client?

A REST (representational state transfer) client is a tool or method to aid communication between different online services via standardized application programming interfaces (REST or “RESTful” APIs). A REST client is a tool or app that can natively access REST services and conforms to the constraints of REST architectural style to create and interact with RESTful web services.

As a software architectural style, REST defines a set of constraints to be used for creating Web services. These web services allow the systems making a request to access and manipulate textual representation of web resources. They do this by using a uniform and predefined set of stateless operations.