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

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.

The Complete Continuous Testing Platform Any test. Any device. App quality without limits.

Test, scrape, generate, and automate without the pain and expense of hosting your own headless browsers.

Playwright enables reliable end-to-end testing for modern web apps.

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.