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

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

Postman is an API platform for building and using APIs. Postman simplifies each step of the API lifecycle and streamlines collaboration so you can create better APIs—faster.

Puppeteer is a Node.js library which provides a high-level API to control Chrome/Chromium over the DevTools Protocol.

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.

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