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

Professional software tool for HTTP testing and debugging

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

Jest is a delightful JavaScript Testing Framework with a focus on simplicity.

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.

Checks web UI for browser compatibility (Compliance with Can I Use?)