RapidAPI for Mac is a full-featured HTTP client that lets you test and describe the APIs you build or consume. It has a beautiful native macOS interface to compose requests, inspect server responses, generate client code and export API definitions.

Real API Design-first Development Platform Design. Debug. Test. Document. Mock. Build APIs Faster & Together.

Mockoon is the easiest and quickest way to design and run mock REST APIs.

Burp or Burp Suite is a set of tools used for penetration testing of web applications. It is developed by a company named Portswigger who make freely available a Web Security Academy which has a range of lessons on penetration testing.

Design, debug, and test APIs locally or in the cloud

Requestly is an open-source tool that simplifies API development, testing, mocking, and integration for developers and QAs.