to a fault vs too

to a fault and too both are adverbs.

Word	Noun	Adjective	Verb	Adverb
to a fault	No	No	No	Yes
too	No	No	No	Yes

As adverbs, to a fault and too are synonyms defined as:

Other synonyms of to a fault include excessively, overly.

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