need recommendations accurate online ruler for measuring on screen

Hey everyone!

I’m looking for a reliable and accurate tool to measure objects directly on my screen. I’ve tried a few browser-based options, but I’m not sure which one is truly the best. Can anyone recommend the best online ruler for screen use that works well on both Windows and Mac?

It would be great if it's adjustable for different screen sizes and easy to use. Bonus points if it’s free and doesn’t require downloads. I appreciate any suggestions or personal experiences you can share.

Thanks in advance for your help!