
using both /roll and /r if you leave off the # of dice to roll (like "d6") always produces a maximum for that die. So "/roll d20" will always produce a 20. "/roll 1d6" produces a pseudo random as expected.
Since it is very common to only have to roll 1 die (initiative, saving throws, to-hit, etc), I would recommend allowing the user to shortcut the # of dice rolled format and be able to "/roll d6".