RPG dice roller

It means roll four six sided dice and keep the three highest. It is the most common way to roll ability scores in tabletop RPGs, because dropping the worst die pulls the results up without capping them.

The notation has four parts. The number before the d is how many dice, the number after it is how many sides, then an optional rule, then a modifier. kh keeps the highest, kl keeps the lowest, dh drops the highest and dl drops the lowest.

So 2d20kh1 is rolling with advantage, 2d20kl1 is rolling with disadvantage, and 4d6dl1 is the same as 4d6kh3 written the other way around.

It uses the cryptographic random generator built into your browser, not the ordinary one. In a dice roller the randomness is the product, so there is no reason to use the weaker generator.

It also throws away the draws that would not divide evenly by the number of faces. Without that step a hundred sided die taken from a single byte would give the low faces slightly more often than the high ones. The bias is small, but it would sit exactly where you are trusting there is none.

12.24, not 10.5. This is worth stating because the wrong number is the intuitive one: three dice averaging 3.5 each would give 10.5, but the three you keep are not three ordinary dice.

Keeping the highest changes what each kept die is. They are order statistics, and the tool computes their expected values exactly rather than estimating by simulation, so the average you read is the real one.

Yes. The notation is written into the address bar as you roll, so copying the link and sending it opens the page with the same dice already filled in.

The result itself is not shared, only the dice. Everyone who opens the link rolls their own.