Technical screening questions
Ask for one example per question and listen for specifics.
- How do you version a public API? A good answer: URL or header versioning, deprecation notices and keeping old clients working.
- How do you prevent duplicate processing of a message? A good answer: Idempotency keys or deduplication on the consumer side.
- What do you cache and what do you never cache? A good answer: Read-heavy, slow-changing data; not per-user sensitive data without care; plus invalidation.
- How do you handle a database that is becoming the bottleneck? A good answer: Indexes, query plans, read replicas, then partitioning.
- How do you secure an API? A good answer: Authentication, scoped authorization, input validation and rate limits.
Quick screening questions
Use these when you have only a few minutes.
- How many requests per second did your busiest service handle?
- How do you design an API so it can change without breaking clients?
- Describe a production incident on a service you owned.
What separates the levels
Match the level to the requirement before you submit.
- Junior: implements endpoints from a spec.
- Mid: designs services and owns their operation.
- Senior: sets service boundaries and data model for a team.
Red flags
Any of these is a reason to probe further.
- No view on database indexes.
- Has never been on call or read production logs.
- Cannot explain what happens when a request times out.
Tools you should hear mentioned
A Backend engineer with real experience usually names several of these without prompting.
- A web framework (Spring, Django, Express, ASP.NET)
- PostgreSQL or MySQL
- Redis
- Message queues
- Docker
- Logging and metrics tools
Run the call well
Ask for the last project first, then dig into the second or third question. Take notes on versions, team size and outcomes, and record them with the submission so the vendor’s later technical interview does not surprise you.
Frequently asked questions
How long should a Backend engineer screening call take?
Fifteen to twenty minutes is enough to cover the project, three technical questions and availability, rate and work authorization.
Do recruiters need to know the technology?
Working vocabulary is enough. Use the sourcing guide for the role and listen for specifics instead of judging technical depth yourself.