Back-end developer interview practice

Back-end interviews test whether you can build the part of the product users never see but depend on. Beyond algorithms, they ask about data, failure and load, which are the things that break in production.

What do back-end developer interviews ask?

Back-end interviews combine algorithm questions with API design, database modelling and indexing, caching, queues, concurrency and system design. Interviewers ask what happens under load or failure, so practise explaining trade-offs aloud, such as consistency against availability, and the cost of each choice.

Practise a back-end interview

Coding rounds

Expect data structure and algorithm questions in the language you will use on the job, often with a practical flavour: parse and aggregate logs, design a rate limiter, implement an LRU cache, merge intervals. Clean code and tested edge cases matter as much as the algorithm.

Data and APIs

Know how to model data, when an index helps and what it costs on writes, what a transaction guarantees and how isolation levels differ, and how to design an endpoint that is safe to retry. Idempotency, pagination and error handling are favourite probes.

Be ready to explain caching (where, what invalidates it, what happens on a miss storm), queues (delivery guarantees, ordering, dead letters) and the difference between concurrency problems you can solve with a lock and those you cannot.

System design

Senior loops add a design round: a URL shortener, a notification system, a feed, a payments flow. See the system design mock interview page for the structure of a good answer.

Practising here

Role loops on the platform run a voice screen, a coding round and often a system design round, so you can rehearse the full sequence for a back-end role. The live editor runs the common back-end languages, including Java, Go, Python, C# and Kotlin. Your first 3 single-question interviews are free for life, every interview report is free, and a new account also gets 6 welcome credits.

Frequently asked questions

Which language should I use for back-end interviews?

The one the role uses, if you know it. Otherwise pick the language you can write fastest without errors; Python and Java are common.

Do back-end interviews ask about databases?

Almost always: modelling, indexes, transactions and query performance are standard topics.

How is this different from a front-end interview?

Less about UI and the browser, more about data, APIs, concurrency and scale, with the same algorithm fundamentals.