"Zero foolishness" is a phrase that can be used to describe a situation or behavior that is free of nonsense, stupidity or any frivolous behavior. Some similar synonyms that can be used to describe a situation or person that is sensible, rational and serious include: no-nonsense, no-frivolity, seriousness, gravity, sobriety, sanity, prudence, judiciousness, wisdom, and practicality. These words can be used interchangeably to express the idea of seriousness and sensibility. When referring to someone who is sensible and rational, the word "no-nonsense" or "no-frivolity" may be more appropriate. Conversely, when describing a situation that lacks foolishness, the word "sanity" or "judiciousness" may be more fitting.