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What the interviewer is testing
Whether you design agents as systems with limits, checks and observability, rather than trusting a capable model to behave.
Answer framework
- Narrow the scope: a clear task, a small set of well-designed tools, and workflows where steps are predictable.
- Validate at boundaries: schema and business-rule checks on every tool call, idempotent actions and safe retries.
- Bound the loop: step limits, cost budgets, timeouts and loop detection.
- Gate risky actions: human approval for payments, deletions or external messages, and least-privilege credentials.
- Observe and evaluate: trace every step, evaluate full trajectories on a test suite, and review failures in production.
Sample answer
Reliability comes from the system around the model. I start by narrowing scope: one well-defined job, a handful of tools with clear descriptions, and fixed workflow steps wherever the path is predictable, leaving the open-ended loop only where it is really needed. Small per-step error rates compound over a long chain, so fewer and simpler steps matter.
Every tool call passes through validation: arguments against the schema, values against business rules, and the user's permissions. Actions are idempotent where possible, so a retry does not refund twice. The loop has a step limit, a cost budget and timeouts, and it detects repeated calls. Anything irreversible, such as sending money, deleting data or emailing a customer, needs explicit human approval, and the agent's credentials allow only what the task requires.
Then I make it observable. Every run is traced: prompts, tool calls, arguments, results, cost and latency. I keep a suite of realistic tasks and score whole trajectories, not just final answers, including whether the agent used the right tools and stopped correctly. Production failures are reviewed and added to that suite.
Likely follow-ups
Common mistakes
- Giving an agent broad tools and credentials for convenience.
- No step, cost or time limits.
- Letting the model take irreversible actions without approval.
- Evaluating only final answers, not trajectories.
- Having no tracing, so failures cannot be diagnosed.
The 0 to 1 AI Engineer Interview Playbook covers the answer frameworks, system-design walkthroughs and an 8-week plan.
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Related questions
Based on question #45 in the full question bank.