18Software Engineering · Interview Prep · Free
Backend Developer interview questions — and how to answer them.
These are the questions Backend Developer candidates are most likely to face, from openers to the hard ones — each with a note on what a strong answer covers. Want more, tuned to your level? Use the free generator below.
What interviewers look for in a Backend Developer
- Concrete examples of systems you've built, with the trade-offs you weighed
- How you debug — the process, not just the fix
- Collaboration signals: code review, disagreements, mentoring
Likely Backend Developer interview questions
1. Tell me about a backend project you've built. What was your role and what technologies did you use?
Discuss specific technologies, your contributions, and measurable outcomes or lessons learned.
2. What programming languages are you most comfortable with, and why do you prefer them?
Name 2-3 languages with concrete reasons; mention recent projects using each.
3. Explain the difference between SQL and NoSQL databases. When would you use each?
Discuss trade-offs (ACID vs. eventual consistency), scalability, and provide real use-case examples.
4. Describe your experience with RESTful APIs. How do you design them?
Cover HTTP methods, status codes, versioning, pagination, and principles like statelessness and resource orientation.
5. Tell me about a time you had to debug a production issue. How did you approach it?
Show systematic methodology: logs, monitoring, hypothesis-testing, root cause analysis, and communication.
6. How do you handle authentication and authorization in your applications?
Discuss JWT, OAuth 2.0, session management, password hashing, and separation of concerns.
7. What's your experience with caching strategies? How do you decide what to cache?
Mention Redis/Memcached, cache invalidation strategies, TTL, and trade-offs between consistency and performance.
8. Describe a system you've designed that needed to scale. What bottlenecks did you identify and how did you address them?
Discuss load testing, database indexing, horizontal/vertical scaling, microservices, or async processing.
9. How do you approach testing in backend development? What's your experience with different testing types?
Cover unit, integration, and end-to-end testing; mention frameworks, CI/CD pipelines, and test coverage goals.
10. Walk me through how you'd design a system to handle 1 million concurrent users. What architectural decisions would you make?
Address load balancing, database sharding, caching, CDN, async queues, monitoring, and database optimization.
11. Explain your understanding of microservices architecture. What are the challenges and how do you address them?
Discuss service decomposition, inter-service communication, data consistency, deployment, observability, and trade-offs.
12. Tell me about a time you disagreed with a technical decision made by your team. How did you handle it?
Demonstrate respectful communication, data-driven reasoning, willingness to learn, and collaborative problem-solving.
Want to practice answering live with scored feedback? Try the Mock Interview Coach.
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