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By the Ace Coach team, built with the best speech coaches · Updated
What these interviews test
O*NET's profile of software developers lists tasks such as analyzing user needs and requirements, modifying software to correct errors and improve performance, and conferring with others on design and project limits. Interviews mirror that: they test whether you can design something sensible, find a fault and explain your reasoning to people who did not write the code.
Most rounds are talked through, not typed. Interviewers listen for how you handle unknowns, whether you ask clarifying questions and whether you can state a trade-off in a sentence. Practice stating your assumptions, asking about missing requirements and naming one trade-off before you choose an approach.
10 questions and how to answer them
1. “Design a URL shortener.”
What they're checking: Whether you clarify requirements before drawing boxes and can reason about scale and trade-offs.
How to answer: Ask about traffic and read-versus-write ratio first, then give a simple design, and name one trade-off, such as hash collisions against a counter service.
2. “Walk me through a hard bug you tracked down.”
What they're checking: Your method for debugging, not just the fix.
How to answer: Say how you narrowed it: what you ruled out, which tool showed the cause and what you changed so it can't recur, such as a test or an alert.
3. “Tell me about a technical decision you'd make differently now.”
What they're checking: Honesty and learning from your own work.
How to answer: Pick a real design choice, name what you missed at the time, and say what signal would have caught it. Full answer guide
4. “How do you review someone else's pull request?”
What they're checking: Whether you balance quality and team speed, and give feedback kindly.
How to answer: Describe what you look at first (tests, correctness, naming) and say you separate must-fix from nit, and ask questions before asserting.
5. “Explain a complex system you built to a non-technical person.”
What they're checking: Plain-language communication.
How to answer: Use one analogy and one concrete outcome, such as page load time, and avoid naming frameworks.
6. “How do you decide between building and buying?”
What they're checking: Judgment about cost, risk and focus.
How to answer: Talk about maintenance cost over two years and whether the thing is core to the product; give one real example.
7. “Tell me about a disagreement with a teammate over an approach.”
What they're checking: Whether you can argue with evidence and then commit.
How to answer: Show you proposed a small experiment or benchmark to settle it, and backed the decision afterwards. Full answer guide
8. “How do you keep a codebase maintainable as it grows?”
What they're checking: Habits for the long term, beyond shipping features.
How to answer: Mention concrete practices you use: tests around risky code, small pull requests and deleting dead code, with one example.
9. “Why do you want to work here?”
What they're checking: Real interest in the product and team.
How to answer: Name something specific from their engineering blog, open source work or product. Full answer guide
10. “Tell me about yourself.”
What they're checking: A clear summary of your experience and direction.
How to answer: Lead with the kind of systems you've worked on and one result, such as latency cut or an outage avoided. Full answer guide
How to prepare
- Talk through problems aloud. Solve three design questions out loud, narrating requirements, design and trade-offs. Silent practice hides the rambling.
- Prepare a debugging story. Write the five steps from symptom to root cause to prevention.
- Pick three projects. For each know the problem, your part, a number and what you'd change.
- Read the product. Use it, then find one engineering decision you can ask about.
Then say your answers out loud. In an AI mock interview the interviewer asks your role's questions and follows up, and you see where you rambled, rushed or hedged.
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