Backend Developer interview questions
Grouped by interview stage, with what a strong answer actually sounds like — the part most question lists leave out.
When interviewing a backend developer, structure questions by stage and assess against the role's actual requirements. Backend developers build the services, APIs and data layers behind a product. The questions below cover screening through final round, each with what a strong answer sounds like and the warning signs of a weak one.
How to use these
Pick four to six for a 45-minute interview — not all 7. A well-followed-up question takes six to eight minutes, and the information is almost always in the follow-up rather than the first answer. Ask the same core questions of every candidate so you can actually compare them; vary the follow-ups.
Screening questions
Describe an API you designed. What would you change about it now?
Why ask it: API design mistakes are expensive because consumers depend on them.
A strong answer: Specific regret about naming, granularity or error handling, and why it mattered later.
A weak answer: Describes endpoints with no reflection on design.
How have you handled a schema change on a large table in production?
Why ask it: A well-defined problem with real consequences, and a strong experience filter.
A strong answer: Backwards-compatible steps, backfill strategy, awareness of locking behaviour.
A weak answer: Runs the migration and hopes, or has never done one.
Technical questions
A downstream service starts failing intermittently. How do you make your service resilient?
Why ask it: Distributed failure handling is where backend seniority shows.
A strong answer: Timeouts, retries with backoff and jitter, circuit breaking, idempotency, graceful degradation.
A weak answer: Retry immediately, forever — which converts a partial outage into a full one.
How do you think about idempotency?
Why ask it: Distinguishes people who have operated payment or messaging systems from those who have not.
A strong answer: Explains why retries make it necessary and how they implement keys.
A weak answer: Unfamiliar with the concept in practice.
What is your approach to handling secrets and credentials?
Why ask it: Cheap to ask, and the failure mode is severe.
A strong answer: Secret manager, no secrets in source or logs, rotation, least privilege.
A weak answer: Environment variables committed to the repo.
Final questions
Tell me about an incident you were on call for.
Why ask it: Operating a system teaches things building one does not.
A strong answer: Clear timeline, how they mitigated before diagnosing, what the follow-up changed.
A weak answer: No operational experience, or blames another team with no follow-up.
How do you decide what to log and what to alert on?
Why ask it: Over-alerting is as damaging as under-alerting, and few people think about it.
A strong answer: Alerts on symptoms users feel, not causes; keeps pages actionable.
A weak answer: Alerts on everything, or has never configured any.
Red flags for this role
- No production operational experience
- Cannot discuss failure modes
- Casual about credentials
What a backend developer actually does
Backend developers build the services, APIs and data layers behind a product. The work is dominated by correctness, failure handling and the cost of changing decisions once data has accumulated behind them.
See the full backend developer job description, including how to assess each requirement.
Generate questions specific to your role — and that account for what previous interviewers already asked — with the free interview question generator.