Harmlessness charted at number 11 on the Heatseekers Albums chart,[10] and at number 46 on the Independent Albums chart.[11] Upon release, the album received critical acclaim. At Metacritic, which assigns a normalized rating out of 100 to reviews from specialized critics, the album received an average score of 84, based on 6 reviews. Stereogum placed the album at number 13 on their top 50 albums of 2015 list.[12] James of Stereogum wrote: "It's not the kind of music that will change the world, but it might just change your life."[12] Aaron Mook of AbsolutePunk wrote: "Harmlessness is ambitious and intimidating in scope; it is not an easy listen, but with the right amount of time and dedication, it is easily one of the most rewarding listens of 2015." "January 10th, 2014" appeared on a best-of emo songs list by Vulture.[13]
In 2017, Harmlessness placed seventh on Spin's list of the emo revival's 30 best albums, with writer Ian Cohen dubbing it "one of the most stunningly accomplished indie rock records of the past decade."[14] Several months later, Cohen called it "an astonishing redirection" for indie rock, seeing it anticipate the genre's impending fusion of the late 90'sPacific Northwest scene's "experimental and expanse" with mid-00sCanadian indie's "grandeur" that would give way to the emo revival.[15] In 2021, Exclaim!'s Adam Feibel wrote that the album had "frequently been held up as [the band's] crowning achievement".[16]
