D&D 5E Formula for creating Warlock invocations

[TrueBagelMan]

So for warlock invocations I think there is a pattern for the invocations that give you a spell. From looking at it I noticed the following:

•The Invocation must be of a level you can cast, otherwise it must have a level requirement for the Invocation.

•The spell can not heal, or deal damage. Temporary hit points are excluded from this rule.

•Spells can not be higher then 5th level, and if they are 5th level they must have a limitation.

•Spells that have a direct combat utility to them, such as Polymorph and Bane, uses a warlock spell slot and is usable again after a Short rest.

I probably didn’t get half of the possible rules, but the point of this is so DMs can check if a homebrew invocation isn’t broken.

 

[Fenris-77]

I think there's also a level component to the split between at will casting and limited castings.

It shouldn't be that hard to compare a HB invocation to the extant models to see if it's OP or not, even without a precise formula. Unless you've gone right off the script of course, at which point the formula won't help you anyway.

 

[Shiroiken]

I think the combat utility ones that use a warlock spell slot should recover on a short rest. This makes them similar to learned spells, but still limits them to once per combat. Making them once per day has made them much less appealing compared to others available.