When you shop for items at a vendor or the Auction House and you hover over an item, you get a comparison tooltip showing the “currently equipped” item too. This AddOn adds such a feature everywhere in the game where you can hover over items, such as in your bags, in the loot window or on the reward page of a quest. You also receive comparison tooltips when clicking an item link in the chat box.
The AddOn is enabled by default. Type “/equipcompare help” for further usage information.