Which is your favorite tool for web developing that a few people know about ?

I use something similar, ColorPick chrome extension, and use it every day. Maybe not my favorite tool, but https://www.colorsandfonts.com/ really helps us find font families and suitable color themes when starting a new project or revamping a site.

Readymag.com This is by far the most underrated site builder. Our site was built using this: https://magicmorning.co/ It's much easier to use than squarespace or wix, and it's way more flexible / powerful.

Interesting questions. Not sure if few people know about it. But recently, I started using BrowserStack - https://www.browserstack.com/ to test the application in different mobile configurations. Pretty happy with the overall experience.