This is a handy utility that just adds a simple readout to the corner of your page that tells you what the viewport width is. Great for designing a responsive sites in the browser. I don't work with standard breakpoints like some designers. I fix elements on the screen when they need fixing or when they look a little off. This utility makes it easy to find a good breakpoint for your media queries.
This plugin requires jQuery.
Just add the viewport_monkey-v1.js file to your HTML Then monkey will be added to the bottom of your viewport.
Use the "px" button to switch between Pixels and EMs and the arrow buttons to move the Monkey around the screen.
Example can be found at jmorgan.ws/viewport_monkey