DRList-1.0 (Classic, TBC & Retail)
Library that contains (hopefully) the most up to date diminishing returns categorization. This is purely the diminishing return data itself with API's to determine if a spellID has a diminishing return, if it diminishes in PvE and the category it diminishes in. You will have to keep track of actual DR timers yourself.
This addon is a rewrite of DRData-1.0 by Adirelle which is no longer maintained.
DRList is updated to seamlessly support all official World of Warcraft clients. (Classic, TBC, Wotlk, Retail)
More info at project's repository: https://www.github.com/wardz/drlist-1.0