truthful
She would not comment on the truthfulness of her original statement.
We will analyze the data to determine the truthfulness of their claims.
He didn't doubt her truthfulness.

SMART Vocabulary: related words and phrases

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