Professional software tool for HTTP testing and debugging

API Testing Platform that automatically generates unit test cases with dependency mocks from API calls

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

ReadyAPI is a low-code API testing platform for development teams that care about creating test automation across any workflow.

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.

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.