Backend Developer Interview Questions and Answers (2026)

Every question below opens to a full page: a quick answer you could give under pressure, what the interviewer is really probing, how to structure your response, a first-person example answer, and the follow-ups that usually come next. Work through your weakest category first.

Prefer one long read? The full backend developer interview guide covers preparation, process and salary talk in a single article.

Databases

Explain the transaction isolation levels and which one your database...Answer + example Two users edit the same record at the same time. How do you stop one...Answer + example A query got slow after a release. Walk me through how you read the qu...Answer + example A single table has grown to several billion rows and writes are slowi...Answer + example

API Design

How would you paginate a large collection endpoint, and why not just...Answer + example You need to make a breaking change to a public API. How do you versio...Answer + example

Messaging

Your message queue guarantees at least once delivery. What does that...Answer + example You need to update the database and publish an event. How do you keep...Answer + example

Architecture

An order flow spans payments, inventory and shipping, each with its o...Answer + example You are building a business to business product. How do you isolate o...Answer + example

Reliability

How do you make a service call to a dependency that might be slow or...Answer + example Traffic doubles and your service starts queuing requests until everyt...Answer + example

Performance

Security

How should passwords be stored, and what would you flag in a review i...Answer + example How do you design authorization for a system where permissions vary b...Answer + example

Scenario

Your API starts returning timeouts under load, but the database CPU i...Answer + example A service gets killed for running out of memory every couple of days....Answer + example You need to pull one capability out of a large monolith into its own...Answer + example Users need to upload files up to two gigabytes. How would you design...Answer + example You need to populate a new column across two hundred million existing...Answer + example You run six instances of a service and need a nightly job to run exac...Answer + example

Tooling

How do you test code that talks to a database and an external API?Answer + example How do you stop a backend change from breaking the clients that consu...Answer + example

Process

How do you decide what to alert on for a backend service?Answer + example How do you roll out a risky backend change safely?Answer + example

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