candid
He requested anonymity so that he could talk candidly.
Readers presume the writer of a blog is trying to give useful, thoughtful information as candidly as possible.
Candidly speaking, if I were him, I would not have waited this long.
He candidly judged himself a bad fit for the job.

SMART Vocabulary: related words and phrases

Honesty, openness & sincerity
above board
anti-corruption
artless
artlessly
artlessness
earnest
honestly
in all honesty/seriousness/truthfulnessidiom
in good faithidiom
integrity
joking apart/asideidiom
let's face itidiom
sincerely
stainless
straight arrowidiom
straight upidiom
straightforward
the straight and narrowidiom
transparency
upright