In all honesty
Definition 1 of 1
Pro Tip 1/3Emotional Weight
Conveys strong personal feeling or a serious tone when sharing thoughts. 
In all honesty, that movie moved me to tears.
Pro Tip 2/3Personal Reflection
Indicates reflection and sincerity before expressing one's own truthful opinion. 
In all honesty, I think we could have tried harder.
Pro Tip 3/3Preempt Disagreement
Prepare listeners for a potentially unpopular or contrary viewpoint. 
In all honesty, I don't agree with the mainstream views on this topic.