This magical piece of markup monkery will make your mission to muster magnificent missives on your monitor much more manageable.
"You know, for grids." #obscurefilmreferences
This plugin allows you to overlay a 12 or 16 column fluid grid to check your positioning when developing fluid or responsive sites.
It also assists you by overlaying lines based on your theme's line height so that you can correctly set your vertical rhythm and line up all of your typography to a baseline grid like the titan of typography that I'm certain you are.
One should be aware that this is a plugin primarily promoted to pixel pushers and isn't for production use. You would do well to know quite a bit about CSS and you should know how your theme is laid out in the HTMLs before using this plugin.
Much to my deep sorrow, it is but a certainty that this fine piece of positional plugin prowess won't work with IE 8 and below (but, surely, one would not be so foolish as to create sites using IE as a development browser) as it requires the magnificent
background-size: 100% CSS3 property to be present. Which in IE, to my great distress, it's not.