Is ONE PIECE episode 381 filler?
Canon No, episode 381 of ONE PIECE is canon.
#381
A New Crewmate! The Musician, Humming Brook!
新たな仲間！音楽家・鼻唄のブルック
Aired 14 Dec 2008
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.