The list below contains sites providing tooling I use in my day-to-day tasks as a web developer. I will keep it up to date.
https://developer.mozilla.org/
Whenever I google “how to accomplish xyz in html/css/js” I use this site as reliable source
“Can I use” provides up-to-date browser support tables for support of front-end web technologies on desktop and mobile web browsers.
build, test and debug regular expressions
https://youmightnotneedjquery.com/
Whenever I stumble accross legacy jQuery code, this site can help in finding out how to replace it