Is it possible to make LaTeX mark overfull boxes in the output?

Is it possible to make LaTeX mark overfull boxes in the output, for example by drawing red rectangles in the PDF where the boxes overflow? The purpose -- to more easily "see" where the problems are in the output.

• \documentclass[draft]{article} – David Carlisle Oct 3 '12 at 10:29
• This is the duty of the draft option to \documentclass – egreg Oct 3 '12 at 10:30
• Out of curiosity: are there other visual warnings available? – Christian Lindig Oct 3 '12 at 11:05
• @ChristianLindig unfortunately, not really. You cannot visualize underfull \hbox, nor over/underfull \vbox nor over/underfull \vbox while \output is active. You have to read the .log to find these. – yo' Oct 3 '12 at 11:27
• @ChristianLindig: Unrelated to overfull boxes, there are packages that provide visual debugging/warnings. Some are even colored :-) – ℝaphink Oct 3 '12 at 11:54

As David Carlisle and egreg said, you can use the draft option in most classes.
If you wish to do it by hand (for example, you need a final option to check for another package's rendering) or tune it, you can use
\overfullrule=1mm

• You're my hero. :-) Microtype was turning off its stuff because of [draft], which apparently can have significant effects on the output. – EvanED Aug 27 '13 at 17:15
• @EvanED Just for the sake of completeness, you can pass the final option to the microtype package to make it do its thing even in draft mode. I always do this because frankly the whole display overfull boxes thing is completely useless if it doesn't respect microtype's changes. – Christian Mar 20 '14 at 1:48