IconVault's Cascade Debugger answers the eternal question: why is this style not applying? Paste your CSS rules, type the target selector you are debugging, and the tool lists every matching selector with its specificity score in (ID, class, element) form. For each CSS property it shows all competing declarations and highlights the winner, with the reason: higher specificity or later in source order.

!important declarations are ranked above normal ones, exactly like the browser does. The specificity engine is hand-written and handles IDs, classes, attributes, pseudo-classes, pseudo-elements and :not() correctly. The honest caveat: matching is a static approximation of the selector's last compound, not a live DOM inspector, so treat it as a logic check. Free and runs fully in your browser.