I just ran through some tests on the character sheet for d100 rolls and it doesn't seem to be programmed properly.

10 + 0 (d10) = 10....  but it really should calculate as 10 + 0 (d10) = 20.

90 + 0 (d10) = 90.... but it really should be the coveted result of 100.

It seems like the code is treating the d10 incorrectly in the calculations...so 00 + 0 = 0 (instead of 10) right now.  The d10 should always be treated like a d10 so that a 0 = 10 on it.

https://dicedungeons.com/blogs/inside/how-to-read-d100-roll

Or does the die roller interpret 00 + 0 = 100?  I guess it would would still allow for 1-100 then.

D&D Beyond is using RAW from the Basic Rules:

Percentile dice, or d100, work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice numbered from 0 to 9. One die (designated before you roll) gives the tens digit, and the other gives the ones digit. If you roll a 7 and a 1, for example, the number rolled is 71. Two 0s represent 100. Some ten-sided dice are numbered in tens (00, 10, 20, and so on), making it easier to distinguish the tens digit from the ones digit. In this case, a roll of 70 and 1 is 71, and 00 and 0 is 100.

Getting a roll of 10+10= 100 is the exception to the rule that one die is the tens place and the other die is the ones place, because the other part of the rule is that you can't roll a 0. If you're seeing a roll with a total of zero that is an error, but otherwise it's performing as intended. The link you provided is not following RAW to determine a roll of 100.

If 00 and 0 is 100 what is 10 then? 10 and 0? and 9 is then 00 and 9? So 00 and 0 counts as 10's but as 0 in all other cases?

Quote from miniwolf >>

If 00 and 0 is 100 what is 10 then? 10 and 0? and 9 is then 00 and 9? So 00 and 0 counts as 10's but as 0 in all other cases?

 There are two ways to read a d100 roll when done using a d10 and a d%

1. The d10 is always read as 1 to 10 (with 0 being 10) and the d% is always read as 0 to 90 (in increments of 10 with 00 being 0). This means that if you roll a 0 and and a 60, the result is actually 70 because it's 10 + 60. Alternatively, 0 and 00 is 10 because it's 10 + 0
2. The d10 is read as 0-9 and the d% as 0-90 (in increments of 10 with 00 being 0) with the exception of 0 + 00 = 100. This means that there's less math involved because you can read the dice literally; 0 and 20 is 20, 4 and 60 is 64.

D&D Beyond uses method 2, which is the method described in the Basic Rules

Percentile dice, or d100, work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice numbered from 0 to 9. One die (designated before you roll) gives the tens digit, and the other gives the ones digit. If you roll a 7 and a 1, for example, the number rolled is 71. Two 0s represent 100. Some ten-sided dice are numbered in tens (00, 10, 20, and so on), making it easier to distinguish the tens digit from the ones digit. In this case, a roll of 70 and 1 is 71, and 00 and 0 is 100.