25 Software Engineer Interview Questions

Walk me through how you would design a URL shortening service like bit.ly from scratch.

How do you decide between writing a new abstraction and reusing an existing one?

Describe a bug you spent more than a day tracking down. How did you approach it?

What's the difference between concurrency and parallelism? Give a real example from your work.

How do you ensure the code you write is maintainable by someone who has never seen it?

Explain the CAP theorem and when you would prioritize consistency over availability.

How would you migrate a monolithic application to microservices without downtime?

Describe your approach to writing unit tests. What do you test and what do you skip?

What strategies do you use to optimize a slow database query?

How do you handle technical debt in a fast-moving team?

Walk me through your code review process — what do you look for and why?

How would you design a rate limiter for a public API?

Tell me about a time you disagreed with a technical decision. How did you handle it?

What's your approach to estimating the complexity of a new feature?

How do you stay current with new technologies without getting distracted by hype?

Describe a situation where you had to make a trade-off between performance and readability.

How would you design a notification system that handles millions of users?

What's the most complex system you've built, and what would you do differently today?

How do you approach debugging a production issue with limited logging?

Explain the difference between REST and GraphQL — when would you choose each?

How do you handle breaking changes in a public API?

What CI/CD practices do you consider non-negotiable on a healthy team?

How would you implement distributed locking across multiple services?

Describe your experience with observability — metrics, logs, and tracing.

If you had to onboard a junior engineer to your codebase in one week, what would you prioritize?