Application Programming Interfaces are the connection structure between different systems or levels of an application. Applications generally have three levels: a data level, a service level (API), and a presentation level (UI). The API level contains the business logic of an application: the rules by which users can interact with the application’s services, data, or functions. Since the API or service level directly affects the data layer and the presentation layer, this is the ideal point for continuous testing for quality control and development teams. Although traditional testing has focused on the user interface, the benefits of API testing are becoming increasingly known. Although there are many aspects of API testing, it is usually necessary to make requests to one or sometimes multiple API endpoints and review the response, either for performance or security reasons, functional fixes, or simply a status check. While the UI test may focus on verifying the appearance of a web interface or on the operation of a specific payment button, the API test places much more emphasis on testing business logic, data and security responses, and performance bottlenecks.