Dice notation
Tabletop games write dice as NdX: N is how many dice and X is the number of sides. 3d6 means roll three six-sided dice and add them up (3 to 18). A d20 decides most checks in Dungeons & Dragons, and d100 (percentile) gives a number from 1 to 100.
Fair rolls
Every die uses your browser's cryptographic random number generator with rejection sampling, so each face is exactly equally likely — no modulo bias. Six-sided dice are drawn with pips like real dice; other dice show the number.
Roll history
Each roll is listed with the individual dice and the total, newest first, so you can check what came up earlier in the game. Your dice choice is remembered in this browser.