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

Fully integrated API and web service testing capabilities that automate end-to-end functional API testing.

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.

Professional software tool for HTTP testing and debugging

Streamline your API testing, integration testing and test data management.

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