Guides
The mechanics behind the numbers, read from the game's code rather than guessed from play. Each guide links to the tool that runs the same math.
Stats explained What every stat does and how it rolls on gear
Item levels How item level, required level and affixes are set
Loot and rarity Drop tables, rarity odds, ancient and black mist
Upgrading gear Upgrade odds, sockets and salvage
Paragon Levels past 70 and where the points go
Patch notes What each update changed, old numbers next to new