12 Rules for Building AI Agents That Survive Production

I sat the Claude Certified Architect exam expecting questions about model parameters, context limits, and API flags. I got something else. The exam barely tests trivia. It tests judgment: given a broken agent and four plausible fixes, which one actually addresses the root cause? The interesting part was how few ideas the whole thing rests on. The same handful of rules kept deciding the "right" answer, and they are the same rules that decide whether an agent holds up once real users touch it. Below are the twelve I kept running into, plus the four traps that look like solutions and are not. This is my own study material, derived from publicly available exam guidance. It reflects how I build, not an official Anthropic position. The twelve rules Enforce determinism in code, not in prompts If a rule has to fire every single time, it is not a job for a prompt. A prompt is a suggestion the model usually follows. "Usually" is not a guarantee. When you need a guarantee, put it in a hook, a gate, or an allowlist. Code enforces. Prose requests. Pick the cheapest fix that hits the root cause Before you build a subsystem, try the levers that cost minutes: a sharper tool description, an explicit acceptance criterion, a config change. Most "we need to build X" moments dissolve once you test the cheap fix first. Reach for the classifier only after the one-line change fails. Bad tool selection? Start with the descriptions When an agent keeps picking the wrong tool, the description is almost always the culprit, not the model. Tool descriptions are the primary signal the model uses to choose. Rewrite them to say exactly when to use the tool and when not to, before you go anywhere near few-shot examples. Over-engineering is almost always the wrong answer Narrowing scope and improving the prompt beat a new subsystem far more often than engineers expect. Every subsystem you add is one more thing to debug, monitor, and keep in sync. Complexity is a cost you pay forever, not once. A bigge