in brief vs briefly

in brief and briefly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
in brief	No	No	No	Yes
briefly	No	No	No	Yes

As adverbs, in brief and briefly are synonyms defined as:

Other synonyms of in brief include concisely, in short, shortly.

in brief (adverb)	briefly (adverb)
in a concise manner; in a few words	for a short time
	in a concise manner; in a few words