Stop using print statements: How do you actually diagnose broken agents?

How do you debug your AI agents when something goes wrong? I am currently working on building AI agents, and I am finding traditional software debugging methods completely useless here. When code crashes, you get a stack trace. But when an agent goes off the rails, it usually doesn't crash—it just fails quietly, hallucinates, or outputs completely unexpected results without throwing any errors. I feel like I am flying blind just using print statements and reading raw terminal logs. I want to know how the community handles this. Could you explain: 1.What is the very first thing you do the moment you realize your agent is not behaving correctly? What tools, frameworks, or custom setups are you using specifically to see exactly what your agent is doing at each step? How do you actually verify that a fix you made to a prompt or workflow doesn't accidentally break something else? Please explain your setup and how you actually track down and fix these abstract issues. I would love to hear your experiences and methods!