The only one I can think of is "pronunciation", but that one is more related to the way you say it rather than to the way you write it.
"The state or quality of being grammatical," or "grammatical correctness" is known as:
And Mithrandir has provided the adjective form in Mithrandir's answer above.
Grammatical correctness is also known as grammaticality.
Grammatical correctness as related to the way you write is also known as grammaticality.
"In...linguistics...a grammaticality judgement...is based on whether the sentence is produced and interpreted in accordance with the rules and constraints of the relevant grammar" ("Grammaticality," Wikipedia).
"The grammaticality of a sentence is things that conform to the linguistic rules or syntactic rules (Fromkin and Rodman 1998:106) ("The Grammaticality versus The Acceptability," Linguistik.)
grammatical without 'correctness'?
of or relating to grammar:
conforming to standard usage:
dictionary.com gives 'antigrammaticalness, noun' as a related word, so I assume that if you remove the 'anti' that gives 'grammaticalness', which should work as a noun.