Senior Engineer Interview Questions and Red Flags That Matter

Most “senior engineer interview questions” lists are trivia — reverse a linked list, explain a closure. Trivia tells you someone studied; it doesn’t tell you they can own a system in production. This is the opposite kind of list: the signals we actually probe, the questions that surface them, and the red flags that fail a candidate even when the code compiles.

It maps to the three stages of how we vet senior engineers — because the point of an interview isn’t difficulty, it’s signal per hour. A founder runs all three.

The underlying principle isn’t ours. Structured interviewing — the same questions and the same rubric for every candidate, scored independently — is the hiring practice with the most evidence behind it. Most senior loops underperform not because the questions are too easy but because each interviewer improvises a different one, which makes the scores incomparable.

Stage 1 — Live coding: watch the debugging, not the answer

We run a 90-minute paired session on a representative problem from the candidate’s target domain — not a puzzle. The code passing is table stakes. What you’re actually reading is how they get there.

Questions/prompts that work:

• “Here’s a function that’s failing intermittently in production. Walk me through how you’d find the cause.” (Watch: do they form a hypothesis, or thrash?)
• “This works. Now make it handle the input being null / the API timing out / the list being empty.” (Watch: do they reach for edge cases unprompted?)
• “Talk me through what you’re thinking before you type.” (Watch: is there a plan, or trial-and-error?)

Red flags:

• Jumps straight to code with no restating of the problem or assumptions.
• Silent for long stretches — a senior narrates trade-offs; silence usually means guessing.
• Can’t debug their own code when you introduce a small failure — memorized the pattern, doesn’t understand it.
• Treats edge cases as an afterthought only when prompted.

Stage 2 — Systems design: trade-offs and failure modes

A 60-minute architecture conversation. Juniors describe the happy path; seniors talk about what breaks and what it costs. You’re listening for hands-on production scars, not textbook diagrams.

Questions that work:

• “Design a system for X. Now — where does it fail first under 10× load, and how would you know before your users do?”
• “You chose a queue / a cache / a second database here. What did that cost you? What did you give up?”
• “This has been in production for two years. What’s the operational pain the diagram doesn’t show?”
• “A junior on your team proposes the simpler version without the cache. Are they wrong?”

Red flags:

• Only describes the happy path; never volunteers a failure mode.
• Adds components (microservices, a message bus, sharding) with no trade-off named — complexity as reflex, not decision.
• Can’t explain why a past choice was made, only what it was.
• Every answer is a pattern from a blog post, none from something they actually operated.

Stage 3 — Communication & ownership: the part that fails “strong coders”

A 45-minute non-technical conversation, and the one that eliminates more otherwise-capable engineers than either technical stage — especially for anyone joining a US team across a timezone. You’re testing written clarity, async habits, and how they behave when they disagree.

Questions that work:

• “Tell me about a time you shipped something you later regretted. What did you do about it?” (Watch: ownership vs blame.)
• “Your lead is set on an approach you think is wrong. Walk me through what you actually say.” (Watch: can they push back diplomatically? Seniors who can’t disagree with leadership aren’t senior.)
• “Write me a two-paragraph status update for a project that’s running two weeks late.” (Watch: clarity, accountability, no burying the lede. If they can’t write a clear async update, they’ll struggle with a remote US client.)
• “What’s a piece of code in production right now you wish you’d written differently?”

Red flags:

• Blames past teams/managers for every failure; owns none.
• Can’t articulate a disagreement without either caving instantly or getting defensive.
• Written English collapses under any complexity — fine for chat, unusable for a design doc.
• Needs a fully specified ticket to move; freezes on ambiguity instead of asking the right question.

The consolidated red-flag list

If you only remember one screen, watch for these across all three stages:

1. Codes before understanding the problem.
2. Describes only the happy path.
3. Adds complexity with no trade-off named.
4. Explains what they built but never why.
5. Blames, never owns.
6. Can’t disagree without caving or getting defensive.
7. Written communication that doesn’t survive complexity.
8. Freezes on ambiguity instead of narrowing it.

Why this is hard to run yourself

None of this is secret — the hard part is running it consistently, on every candidate, with interviewers senior enough to read the signals. That’s most of why hiring at scale drifts toward trivia (it’s cheap to grade) and why marketplaces optimize for catalog size over depth. Our version is the opposite trade: founders run this exact screen on every placement, which caps how many people we can place and is why the engineers we place stay.

If you’d rather not run three stages per candidate for every hire, tell us the role and we’ll present engineers who already cleared it.