Auto roll a d20 when a spell is cast

Is there a way to do either a global damage modifier or some kind of macro that will roll a d20 whenever a character casts a spell?  This is for use to determine a wild magic surge in 5th edition while my players travel through an area which has a chance for a wild magic surge to ocurr.  To take it even a step farther, is there a way one could have a secondary roll occur (d100) if the result of the d20 roll is a 1?

For auto rolling a d100 on a 1 of a d20, there sort of is but its not number or nothing, rather 0 or the d100 For that you can do this [[ [[1d20<1]]d100]] This will roll a d20, see if its less that or equal to 1 (roll success) and roll that many d100 (0 or 1). This will mean it can show either a 0, or the d100 roll. Alternatively, if you have wild magic as a table, you can do that as well using something like this (with Wild-Magic-Table being the name of the table)  [[ [[1d20<1]]t[Wild-Magic-Table] ]] That can output the text of the table if you have it all entered. For adding that to a sheet, depends on which you use. Shaped it is trivially easy to add to spells, just use spell attachers.  Using OGL, no idea of a nice way to do it. I don't use that sheet so maybe someone else can help there.

The Macro works like a charm but I do use OGL so that would be nice to have some way to get it working on their sheets or some way to automate the process so we as a group don't forget.

Make a rollable table for each of the wild magic surge effects and name the table Wild-Magic-Surge Then make a macro for rolling from the table and you can set it so that it is visible to players. &{template:npcaction} {{rname=Wild Magic Surge}} {{name=d100}} {{description=[[1t[Wild-Magic-Surge]]]}}