grammaticalement correct
I don't think that this sentence is grammatically correct.
Je ne pense pas que cette phrase soit grammaticalement correcte.
This sentence sounds natural, but it's not grammatically correct.
Cette phrase sonne naturellement, mais elle n’est pas grammaticalement correcte.
This sentence is grammatically correct.
Cette phrase est grammaticalement correcte.
This sentence seems to be grammatically correct.
Cette phrase semble grammaticalement correcte.