You create a magical zone that guards against deception in a 15-foot-radius Sphere centered on a point within range. Until the spell ends, a creature that enters the spell's area for the first time on a turn or starts its turn there makes a CHA Save. On a failed save, a creature can't speak a deliberate lie while in the radius. You know whether a creature succeeds or fails on this save.
An affected creature is aware of the spell and can avoid answering questions to which it would normally respond with a lie. Such a creature can be evasive yet must be truthful.