Test::tabs scans your project/distribution for any perl files (scripts, modules, etc) for the presence of tabs.

in particular, it checks that all indentation is done using tabs, not spaces; alignment is done via spaces, not tabs; indentation levels never jump up (e.g. going from 1 tab indent to 3 tab indent without an intervening 2 tab indent); and there is no trailing whitespace on any line (though lines may consist entirely of whitespace).