[En] "Less vs fewer" and "continuously vs continually" rule

Can we create a rule to drill down to the root of the errors when “Less vs fewer” and “continuously vs continually” is misused? Maybe simple, but I could not figure out how to do that.

Doesn’t the first fall under countable/uncountable?

I would search for “fewer” followed by a singular noun and “less” followed by a plural noun.

True. But considering the sentence like “To serve the guests I need three glasses of water or fewer” (glasses are countable) I thought that it wouldn’t be that easy to create such rules. The problem is, how the grammar checker detects the noun.