Really, really useful tool for developing the way a web page behaves with responsive CSS and javascript kicking in at different screen widths. I've been wanting this functionality for a long time, so brilliant to have such an easy-to-use and neatly implemented tool available. Many thanks and kudos Luke Peters.

it's a pretty good extension, but when I set for body element text-shadow is used also for extension span element.

Thank you for this! I've been using it for a while and it's a vital part of my workflow :) One tiny quibble if I had to: it does pop up when entering full screen mode on a YouTube video for instance, but that might be unavoidable and it's hardly a big deal

Excactly what I needed. Only three suggestions:
1) don't be shy with the z-index. I installed and I thought it wasn't working until I realized there was a fixed header with z-index 99999 on the site I was testintg.
2) a few size options. I wouldn't mind a tiny one to use always on.
3) use pointer-events: none so we can click through it :)

Safe and does exactly what it says.

A suggestion would be to make an option to make the box stay and not disappear after 1-10 seconds.

Works perfectly for the sites I'm working on. It didn't work for this page of the review due to:

Content Security Policy: The page’s settings blocked the loading of a resource at inline (“style-src”).

But perhaps there's nothing that can be done about it?

Thanks for writing this very much needed extension

Works perfectly, very simple and usefull for web developpers.
Thanx for this extension !

Works perfectly. love that you can change location of values.

Extension did exactly what I wanted but I've had to uninstall it due to it causing the following error in my console:

Error: Permission denied to access property "apply"

No option to change the position of the little popup with the viewport size...