What adjective describes someone excessively ready to find fault or engage in petty criticism?

The adjective "captious" accurately describes someone who is excessively eager to find fault or engage in petty criticism. This term originates from the Latin word "captiosus," which means "deceitful" or "catching." A captious individual tends to nitpick and focus on minor errors or flaws, often to challenge others or to provoke disagreements. This disposition suggests a critical nature that seeks to entrap others in arguments or criticisms, which aligns perfectly with the definition provided in the question.

In contrast, "contumacious" refers to defiance or stubbornness towards authority, which does not specifically imply a propensity for petty criticism. "Defalcate" is a term that means to misuse funds or embezzle, and does not relate to criticism at all. "Cozen" means to deceive or cheat, which again lacks the context of fault-finding. Therefore, "captious" is the most fitting word for someone who is quick to criticize or find fault.