well-formed vs grammatical

well-formed and grammatical both are adjectives.

Word	Noun	Adjective	Verb	Adverb
well-formed	No	Yes	No	No
grammatical	No	Yes	No	No

As adjectives, well-formed and grammatical are synonyms defined as:

well-formed and grammatical: conforming to the rules of grammar or usage accepted by native speakers

well-formed (adjective)	grammatical (adjective)
conforming to the rules of grammar or usage accepted by native speakers	conforming to the rules of grammar or usage accepted by native speakers
	of or pertaining to grammar