Note: This package is no longer maintained because Emacs 23 has this feature integrated into WhitespaceMode. Add ‘lines’ or ‘lines-tail’ to variable ‘whitespace-style’ and customize ‘whitespace-line-column’. – nschum

This mode highlights all characters that cross the 80 character line limit. It is available at at http://nschum.de/src/emacs/highlight-80+/.


The WhitespaceMode of Emacs does a very similar thing, but not exactly the same. It highlights the entire line, when the line is longer than ‘whitespace-line-column’. It would also be nice if we could configure Emacs to show an overlay at column 80, like the one shown at:


To get a overlay marker at column 80 check out FillColumnIndicator.