1- Regex101.com
An interesting tool to debug regular expressions online, but also a great library of useful and ready to use regular expressions. You can choose your favorite flavor of regular expression PCRE, Javascript, Python, or Golang.
2- CanIUse.com
“Can I use” provides up-to-date browser support tables for support of front-end web technologies on desktop and web browsers.
3- Lighthouse
Lighthouse is an open-source, automated tool for improving the quality of web pages. You can run it against any web page, public or requiring authentication. It has audits for performance, accessibility, progressive web apps, SEO and more. Recently you can use Lighthouse to test publisher ads performance.
4- Metatags.io
Meta Tags is a tool to debug and generate meta tag code for any website. With Meta Tags you can edit and experiment with your content then preview how your webpage will look on Google, Facebook, Twitter and more!
5- WhatRuns.com
WhatRuns is a free browser extension that helps you identify technologies used on any website at the click of a button.
