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Backend Developer interview questions & mock practice

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What interview questions are asked for a Backend Developer?

A Backend Developer interview in 2026 runs across 4 rounds — dsa round, language & runtime, database & api design, system design. Below are the most-asked Backend Developer interview questions and a focused prep plan. Rehearse every answer out loud with the free timed practice below before the real one.

REST APIs
SQL
System Design
Caching
Concurrency
Microservices
Security

Free interview practice · Backend Developer

Practise your Backend Developer interview now — free

Step through the 12 most-asked Backend Developer questions one at a time, under a timer, just like the real thing. Jot your answer, then reveal what a strong answer covers. No signup needed to practise.

Time per question

Interview rounds

The Backend Developer interview process

APIs, databases, concurrency and system design — the server-side engineering interview across product companies and fintech.

1. DSA round

Coding problems plus complexity analysis.

2. Language & runtime

Deep dive on your primary language (Java/Node/Python/Go) and its concurrency model.

3. Database & API design

Schema design, indexing, transactions and REST/gRPC API design.

4. System design

Designing scalable, fault-tolerant backend services.

Most-asked questions

Most-asked Backend Developer interview questions

12 of the questions Backend Developer candidates are asked most often in India. Practise answering each one out loud in the timed practice above.

1. Explain the difference between SQL and NoSQL, and when you'd choose each.
2. What is database indexing and how does it speed up queries?
3. Explain ACID properties in a database transaction.
4. What is the difference between REST and GraphQL?
5. How do you handle concurrency and race conditions in your backend?
6. What is a deadlock and how do you prevent it?
7. Explain caching strategies — write-through, write-back and cache invalidation.
8. What is the difference between horizontal and vertical scaling?
9. How would you design a rate limiter for an API?
10. Explain database normalisation and when you would denormalise.
11. What status codes do you return for different API scenarios?
12. How do you secure a REST API (auth, tokens, input validation)?

How to prepare

How to prepare for your Backend Developer interview

Master database fundamentals: indexing, transactions, isolation levels, and query optimisation.

Be able to design a clean REST API: resource naming, status codes, pagination, idempotency and versioning.

Understand your language's concurrency model deeply (threads, async I/O, locks, the GIL if Python).

Practice system design: caching, message queues, sharding, replication and how to avoid single points of failure.

Know security basics cold: authentication vs authorisation, JWT, hashing passwords, and preventing SQL injection.

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Interview prep guides

Backend Developer interview — FAQs

What questions are asked in a Backend Developer interview?

Common Backend Developer interview questions include: Explain the difference between SQL and NoSQL, and when you'd choose each. What is database indexing and how does it speed up queries? Explain ACID properties in a database transaction. What is the difference between REST and GraphQL? Interviews usually run across 4 rounds — DSA round, Language & runtime, Database & API design, System design. Practise them with the free timed practice on this page.

How many rounds are in a Backend Developer interview?

A typical Backend Developer interview has 4 rounds: DSA round (Coding problems plus complexity analysis.); Language & runtime (Deep dive on your primary language (Java/Node/Python/Go) and its concurrency model.); Database & API design (Schema design, indexing, transactions and REST/gRPC API design.); System design (Designing scalable, fault-tolerant backend services.).

How do I prepare for a Backend Developer interview?

To prepare for a Backend Developer interview: Master database fundamentals: indexing, transactions, isolation levels, and query optimisation. Be able to design a clean REST API: resource naming, status codes, pagination, idempotency and versioning. Understand your language's concurrency model deeply (threads, async I/O, locks, the GIL if Python). Then rehearse every question out loud with the timed practice on this page before the real thing.

What skills do I need for a Backend Developer role?

Core Backend Developer skills tested in interviews include REST APIs, SQL, System Design, Caching, Concurrency, Microservices, Security. OnJob shows you exactly which of these skills stand between you and a 100% match on every live Backend Developer job.

Is the Backend Developer mock interview practice free?

Yes. The questions, the answer guidance and the timed practice on this page are free and need no signup. With a free OnJob account you can also take timed role tests and free certification tests. Personalised AI role and skill tests are part of the paid plans.

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Ace your Backend Developer interview

Rehearse every Backend Developer question out loud on this page, then sign in to take a timed role test or a free certification in the OnJob practice hub.

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