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Software Engineer interview questions
Software engineer interviews test whether you can solve a problem you haven't seen, explain your thinking while you do it, and work well with other people. These are the questions that come up most, and how to handle each one.
What interviewers look for
- Problem solving. How you break down an unfamiliar problem matters more than a perfect first attempt.
- Code quality. Readable names, sensible structure and tests you would actually write.
- Trade-offs. Why you chose one approach, and what you gave up by choosing it.
How the interview usually runs
- Recruiter call about your background, salary and timing.
- Coding screen on a shared editor or a take-home task.
- Two to four technical interviews on algorithms, system design and past work.
- Behavioural round with a manager.
Stages vary by company, so ask the recruiter what to expect before you start preparing.
10 Software Engineer interview questions, and how to answer them
1. Walk me through a project you're proud of.
What they want to see: Whether you owned real decisions, not just tickets.
How to answer: Pick one project. Cover the goal, your part, the hardest decision and the result, in about two minutes.
2. How do you find a bug you can't reproduce?
What they want to see: A calm method rather than guessing.
How to answer: Describe gathering logs and timing, narrowing what changed, adding instrumentation and writing a failing test once you have it.
3. What happens when you type a URL into a browser?
What they want to see: How deep your understanding of the stack goes.
How to answer: Go through DNS, TCP and TLS, the HTTP request, the server, and rendering. Offer to go deeper where you know most.
4. How would you reverse a linked list?
What they want to see: Basic data structures and how you talk while coding.
How to answer: State the approach first, mention the three pointers, code it, then test with empty and single-node lists. Give O(n) time and O(1) space.
5. When would you use a hash map instead of an array?
What they want to see: Whether you think in access patterns and cost.
How to answer: Compare lookup, memory and ordering. Give a real example where the choice changed performance.
6. How do you design a URL shortener?
What they want to see: Basic system design: scope, data, scale.
How to answer: Ask about traffic, sketch the API and storage, explain ID generation and caching, then name what breaks first at scale.
7. How do you decide what to test?
What they want to see: Practical judgement about quality.
How to answer: Focus on behaviour that would hurt if it broke, keep most tests fast, and add an integration test for risky paths.
8. Tell me about a time you disagreed with a code review.
What they want to see: How you handle technical conflict.
How to answer: Show you asked why, compared options with evidence, and were happy to change your mind.
9. How do you handle a deadline you know you'll miss?
What they want to see: Honesty and ownership.
How to answer: Raise it early, offer options on scope, and explain how you kept people informed.
10. What would you improve in our product?
What they want to see: Whether you did your homework and think about users.
How to answer: Name one real issue from using the product, say why it matters and suggest a small first step.
A sample answer
Tell me about a time you improved performance.
Our search endpoint had crept up to two seconds at peak. I traced requests and found one query doing a full table scan after a schema change. I added an index, cached the most common filters and added an alert on response time. Latency dropped to about 200 milliseconds, and the same check now runs before every release.
A made-up example to show the structure. Use your own experience and real numbers.Common mistakes
- Starting to code before you've confirmed the problem.
- Going silent while you think, so the interviewer can't follow you.
- Saying "we" throughout, which hides what you actually did.
- Stopping at working code without testing edge cases.
Practise this out loud
Run a mock interview for a Software Engineer role. Questions change every time, you answer by voice or typing, and each answer gets a score with feedback.
Frequently asked questions
How many questions should I prepare for a software engineer interview?
Aim for five project and behavioural stories you know well, then steady practice on common data structures. Stories cover most non-coding questions, so you don't need one for every possible prompt.
Do software engineers still need LeetCode practice?
Many companies still use coding screens, so some practice helps. Ask the recruiter what the format is. If it's a practical task, spend more time building and reading code instead.