I know we don't really like the grammar tag around here. The tag wiki says:
This tag is for grammar questions, but only if you're not certain what other tag to use. If possible, tag as tense, verb, articles, prepositions, or some other more specific tag or tags instead.
Now I think it's a fantastic idea to use more specific tags rather than grammar, but I don't think that grammaticality is much better, just slightly rarer.
The tag grammaticality is about:
Grammaticality refers to whether something obeys the rules of English grammar.
This seems like a great candidate for synonymizing. Tagging a question with grammaticality provides no new information.
I would have proposed a synonym myself, but I have a measly 0 points in this particular tag, so I can't really do anything about it.