Rolling a 1d100 on a Crit

Our GM (DnD 5e) uses random tables on a critical success or failure. Is there a way to add a script to an attack roll when you roll either a 1 or 20? And what would that script look like? Thank you in advance.

That's solid API territory . I think you can use Powercards to roll on a table on a crit or fumble - your GM must have a Pro subscription, and be willing to set up some API stuff. The GM could just have two buttons on their macro bar to roll on the CF and CS tables when one occurs - this doesn't require the API but it does need to be manually activated. This is the simplest method, by far. The macro can be as simple as  /r 1t[table_name] . Presumably when you say "our GM uses random tables" this is already set up in game? If not, the GM will need to add them as Rollable Tables . The critical success part could be automated without API, but you would have to modify every crit damage field in the game (every weapon for every character).

Assuming you're using the 5E by Roll20 sheet, you can add a hidden link in any attack's description. To do so, open up the attack entry on a player's sheet, and in the description section add the following line (for this example I named my table Crit) [Crit](!
/r 1t[Crit]) So if a crit was rolled you'd then click on the word Crit in the attack's description in the chat window, and it will roll on the listed table. In order to link an automatic roll to a critical hit, you'd either need API to access the sheet's coding, or you'd need to do a whole lot of work to make 3 ability entries for each attack: one attack roll, one normal damage, and one crit damage.