Grammaticality refers to whether something obeys the rules of grammar in English. If your question is about grammar itself, please use the "grammar" tag.
Grammaticality refers to whether some word, phrase, or sentence is grammatical; this tag encompasses questions about where the boundary between grammatical and ungrammatical is.
This tag is used for questions that ask whether some particular usage is grammatical, correct, right, proper or ungrammatical, incorrect, wrong, erroneous, a mistake.
If the question is about how the grammar works, about how different grammatical usages, and how they can be used or what they mean, use grammar.