overly vs too

overly and too both are adverbs.

Word	Noun	Adjective	Verb	Adverb
overly	No	No	No	Yes
too	No	No	No	Yes

As adverbs, overly and too are synonyms defined as:

Other synonyms of overly include excessively, to a fault.

overly (adverb)	too (adverb)
to a degree exceeding normal or proper limits	to a degree exceeding normal or proper limits
	in addition