A free browser plugin that helps developers, content editors, & SEO professionals quickly scan webpage for broken links, valid links & potential issues.

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.

SelectorsHub is the Next Gen XPath Plugin & Selectors tool. It supports all kinds of XPath, locators, shadow dom, iframe, svg, dynamic elements, multi selectors generation and xpath error handling. It is a Free community product.

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

Built for developers and testers alike, SoapUI is the only open source tool that covers the entire testing spectrum (functional, security, load, mocking).

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