Instant Interview
FreeIntermediate5 min · 10 questions

Backend Developer Interview Questions

APIs, databases, system design, and security. The questions backend interviews actually revolve around, tested through real scenarios rather than textbook definitions.

APIsDatabasesSystem DesignSecurity
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Question 1
How would you handle breaking changes to a REST API without disrupting existing clients?

Interview preparation guide

Backend Developer interview questions: what to prepare

The quiz above is a quick way to check your knowledge. Before the interview, prepare a specific example for each of these themes: APIs, Databases, System Design, Security. Practise saying your answer aloud, then refine the detail, evidence and outcome rather than memorising a script.

Five questions worth preparing now

  1. Question 1 · API Design

    How would you handle breaking changes to a REST API without disrupting existing clients?

    URL path versioning is explicit, discoverable, and widely adopted. Interviewers want the full lifecycle: versioning, communicating deprecation via Sunset headers, and supporting multiple versions during migration.

  2. Question 2 · Database Selection

    Activity logs are written millions of times a day but queried rarely, always by user ID and date range. Which database?

    Cassandra excels at high write throughput with time-series data partitioned by a key like user_id. The user-plus-date-range pattern maps to its partition model — match the access pattern to the database.

  3. Question 3 · Caching Strategy

    Product listings change a few times a day but get thousands of requests a minute. What do you address first when caching?

    Cache invalidation is famously the hardest part. Interviewers want you to think through how stale data gets detected and replaced. TTL expiry, event-driven invalidation, or cache-aside all show mature thinking.

  4. Question 4 · Concurrency

    Two users occasionally buy the same last-in-stock item simultaneously. How do you frame your solution?

    Optimistic concurrency control handles the common case (no conflict) efficiently and only retries on the rare collision. Distributed locks add latency for every request. Weigh correctness against performance.

  5. Question 5 · Schema Design

    On a social platform where users follow each other, how would you model the "followers" relationship?

    A junction table with composite indexes supports efficient queries in both directions and scales well. The JSON approach breaks down at scale and makes queries expensive. Model around query patterns.

A simple preparation checklist

  • Choose relevant, truthful examples and explain the outcome and learning. Use numbers only when you have them.
  • Use STAR for experience questions: keep the situation brief and spend most of the answer on what you did.
  • Say each answer out loud, then remove jargon, filler and unnecessary background detail.
  • Prepare one thoughtful question about the role, team or priorities for the end of the interview.

Turn knowledge into practice

Use the quiz to identify the theme you need to improve, then rehearse it as a spoken answer and get feedback on your structure, pace and specificity.

Start technical interview practiceCheck a STAR answer