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30 backend engineer
interview questions that actually work.
Pulled from the Neuroworx item bank: nine years of calibration against twelve-month performance outcomes on 14,083 backend engineers. Sorted by stage (screen, assessment, on-site) and level (IC1 to IC5). Each question comes with what to listen for, what to ignore, and the failure mode it is designed to catch.
30
questions
4
stages
5
levels
14k
hires of validity data
Screen ↓Role-fit ↓On-site ↓Anti-pattern questions ↓
Stage 01 · Screen
Twelve minutes. Ten questions.
The screening conversation. Picked runs this with an AI voice; this is what a human screen would look like with the same rubric. Time-box hard. 60 seconds per answer.
10 questions
01
Tell me about the last service you owned past v1. What broke first in production, and what did you do?
ownershipspecificity
Listen for
A specific service. A real failure mode (timeouts, lock contention, queue backup). A fix that names a trade-off.
Ignore
Adjective-heavy answers about "scalable" or "fault-tolerant" with no incident and no metric.
catches · CV inflation. Services they touched but did not own.
02
Pick a part of your current backend codebase you think is wrong. Why has it not been fixed?
judgementpolitics
Listen for
A specific module or schema choice. An honest reason for the not-yet (cost, fear of migration, priority).
Ignore
"Everything is fine." Or a moan about a teammate.
catches · Cannot hold an opinion without making it personal.
03
Walk me through the most recent backend change you took from spec to production.
scopeagency
Listen for
The whole arc, including who they convinced and what they migrated. Specific dates, specific numbers.
Ignore
Tech-stack listing. Stack is downstream of scope.
catches · Engineers who only own the inside of the function.
04
What is the smallest backend decision you have fought hardest for?
convictiontaste
Listen for
A real example. A column type, an idempotency key, a retry policy. They say what they would do differently.
Ignore
Big architecture flexes about microservices. Usually rehearsed.
catches · No discrimination between large and small decisions.
05
Pick a backend service you use daily and tell me how it probably works under the hood.
curiositysystems
Listen for
Reasonable guesses at the boring parts: queues, sharding, cache, write-ahead logs. They name what they do not know.
Ignore
Stack-exchange recital.
catches · Memorised-answer engineers. Stops when the system is unfamiliar.
06
Last time a teammate disagreed with you in a design review. Walk me through it.
commsego
Listen for
A concrete review they remember. Whether they changed their mind and what changed it.
Ignore
"I always listen to feedback."
catches · Defensiveness as a personality trait.
07
What is your favourite production incident you have been involved in?
reliabilitywar stories
Listen for
A specific outage with a real root cause. Their precise role. What they changed about the system after.
Ignore
A dramatic story with no resolution.
catches · Engineers who have never been close enough to production to have one.
08
Tell me about a database or queue you tried and rejected.
tastecritical thinking
Listen for
A genuine evaluation. A specific reason to reject (operational cost, missing primitive, team familiarity).
Ignore
A datastore they are "exploring".
catches · CV as the boundary of what they have considered.
09
How do you onboard onto an unfamiliar backend codebase?
judgementgenerality
Listen for
A sequence: run it, trace one request end-to-end, read the migrations folder, find an old post-mortem, ask one specific question.
Ignore
"I read everything first." Does not scale.
catches · Engineers who freeze without documentation.
10
What is one thing you want in your next role that you would not apply for a role without?
stage fitseriousness
Listen for
Something specific. A particular scale of system, a specific kind of on-call, a specific data model.
Ignore
"Impact." "Growth." "Ownership."
catches · Candidates who are not sure why they are looking.
Stage 02 · Role-fit assessment
A scoped task. A scored rubric.
One realistic task. We score the writeup, not the polish. The candidate has the take-home equivalent of 60 minutes.
8 questions
01
Design a service that ingests 50k events per second and persists each one for at least a year. Sketch components, identify three failure modes, and name what you would build first.
systems designIC3+
Listen for
Capacity reasoning. A real first cut with the boring parts present. Three actual failure modes (backpressure, partition skew, schema drift).
Ignore
A perfect-looking architecture diagram.
catches · Architecture astronauts. Comprehensive on paper, helpless in production.
02
Here is a 250-line handler from a real codebase. Refactor it. Three bullets on what you changed and why.
code qualityIC1+
Listen for
Edge-case handling, transaction boundaries, error paths. The bullets reveal taste.
Ignore
Renaming for the sake of renaming. Adding ceremony.
catches · Cargo-cult cleanups.
03
Pick one of three small bugs we have described. Reproduce locally, write the fix, write the post-mortem. 60 minutes max.
craftIC2+
Listen for
How they reach the repro. What they do not change. The shape of the post-mortem.
Ignore
Time spent on environment setup. We supply a working dev box.
catches · Engineers who cannot name what they do not know.
04
Read this 3-page design doc for a new service. Write three questions for the author and one push-back.
judgementIC3+
Listen for
Questions that show they have read the doc. A push-back that engages with the trade-off the author chose.
Ignore
Stylistic edits.
catches · Engineers who cannot engage with someone else's design.
05
Estimate the daily cost of running this service at our current load. Show your working in three sentences.
cost-awareIC2+
Listen for
Reasonable orders of magnitude. They name their assumptions. They notice when a number is wrong.
Ignore
Spreadsheets. We want the back-of-envelope.
catches · Engineers who only know how to build, never how to estimate.
06
Take this real merge request. Decide if you would approve, request changes, or close. Write the review.
code reviewIC2+
Listen for
Substantive comments on the design choice, the missing migration step, the unhandled error path.
Ignore
Five-line reviews of a 200-line MR.
catches · Reviewers who cannot prioritise.
07
Write the on-call runbook for the service you sketched in question 1.
operabilityIC3+
Listen for
They imagine being woken at 3am. Specific signals, specific commands, specific decisions about when to escalate.
Ignore
Cargo-culted runbook templates.
catches · Engineers who can build but cannot imagine operating.
08
In 200 words, why might the service you sketched in question 1 be the wrong choice?
humilityIC4+
Listen for
Genuine engagement with the alternative. A real "I might have used Kafka" or "I should have started with a cron and a table".
Ignore
A second pitch for the original design.
catches · Lack of perspective on their own choices.
Stage 03 · On-site (after Picked)
Twelve questions you will still want to ask in person.
Picked screens, scores, and shortlists. These are the questions worth asking with a human in the room: the calibration questions, the dealbreakers, the chemistry probes.
12 questions
01
Where, in the work, do you want to grow most this year?
growthmanager fit
Listen for
A specific gap. A plan, even tentative. A name of someone they would learn from.
Ignore
"I want to be a staff engineer." Title-laddering is not growth.
catches · Engineers without a learning agenda.
02
Tell me about a time you disagreed with a manager. What happened?
authoritymanager fit
Listen for
A real disagreement. The mechanics of the conflict, not the moral.
Ignore
"I have never disagreed with a manager."
catches · Engineers who cannot hold opinions in the face of authority.
03
What is the most uncomfortable feedback you have received and what did you do with it?
self-awareness
Listen for
A specific piece of feedback. The change they made. The thing they still struggle with.
Ignore
"I take feedback well."
catches · Defended self-narrative.
04
Walk me through a project you wish had failed faster.
judgementoperating
Listen for
Honesty. A specific moment they could have called it. What stopped them.
Ignore
A pitch for the project being secretly worth doing.
catches · Sunk-cost thinkers.
05
What is a strong opinion about backend systems you have recently changed?
intellectual humility
Listen for
A specific opinion. A specific reason. They name the bug, talk, or person that changed their mind.
Ignore
"My mind is always open."
catches · Closed-loop thinkers.
06
Pick two senior engineers you admire from your last role. What do they do differently?
taste
Listen for
Concrete habits. Habits they have adopted, habits they have not.
Ignore
Pure praise.
catches · Engineers without taste for other engineers.
07
Tell me the last technical thing you read outside your day-to-day stack.
curiosity
Listen for
A specific paper, blog, talk. They tell you what they thought, not just that they read it.
Ignore
A textbook they "always mean to get to".
catches · Engineers who do not think outside their stack.
08
When are you most productive?
operating model
Listen for
A specific time-of-day and environment. A self-aware answer about energy.
Ignore
"I am always productive." Noise.
catches · Engineers without self-instrumentation.
09
Where would you rather be in three years?
careerretention
Listen for
A direction (deeper IC vs people-management) and a reason. Honesty about uncertainty.
Ignore
"Wherever the company needs me."
catches · Drifting engineers.
10
If you join, what would you want your first week to look like?
agencyonboarding
Listen for
A specific plan. Often: shadow on-call, ship a 50-line PR, read three post-mortems.
Ignore
"Whatever you suggest."
catches · Engineers without an onboarding instinct.
11
What would make you leave us within six months?
dealbreaker
Listen for
A specific irritant. A specific working condition. A specific kind of management.
Ignore
"As long as the work is good."
catches · Hidden dealbreakers, surfaced post-offer.
12
What is one question you want to ask our most cynical engineer?
probingcuriosity
Listen for
A real question, usually about a quiet thing: "Why is your test suite slow?" or "What is the gnarliest service?"
Ignore
A softball or a re-pitch of their interest.
catches · Candidates who do not want to know what is wrong.
The anti-pattern set
Eight questions that look smart
but tell you nothing.
"What is your biggest weakness?"
You will get a strength-shaped weakness. We have asked this 47,000 times. It catches no-one. Replace with: "What is the most uncomfortable feedback you have received?".
"Where do you see yourself in five years?"
Either a rehearsed answer or a stalled one. Both useless. Replace with: "Where would you want to be in three years?"
"Tell me about yourself."
Wastes the first three minutes on the CV they already gave you. Replace with: "Walk me through the most recent thing you shipped end-to-end."
"Why this company?"
Generates polished mission-talk. Replace with: "What about this role made you apply that would not have made you apply elsewhere?"
"Are you a team player?"
No-one says no. Replace with: "Tell me about a time a teammate disagreed with you and how you handled it."
"How do you handle stress?"
No-one says badly. Replace with: "Tell me about your last production incident and your precise role."
"How would you reverse a linked list?"
Probes nothing we care about. We removed it from the bank in 2019. Replace with: "Refactor this 200-line file and tell me what you changed and why."
"If you were an animal, which animal would you be?"
You know what we are going to say. Replace with: anything else.
Or, let us ask
We will ask these for you.
By Friday.
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Backend engineer interview questions · Picked.ai