How do we know how much Restful API is? Some developers call it “Not Restful API”, some call it “Partially Restful API”, for some, it is “Fully Restful API”, and for some “It is not REST API at all or they call it SOAP based web service”. Imagine it as a spectrum from Not Restful to Fully Restful API. To know at which level API stand, Richardson introduces a model called Richardson Maturity Model. As the name itself suggests, it tells about the maturity level of REST API.