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Senior engineer project deep dive: trade-offs, scale, challenges, hardest part

LegoraSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenBehavioral & Leadership

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Behavioral question for senior software engineers: lead a 20-minute deep dive into a past project and answer probing questions about trade-offs, operating scale, challenges and the hardest part. It assesses ownership, engineering judgment, use of concrete numbers, and clear technical communication under time pressure.

You are interviewing for a senior software engineer role. The technical screen lasts 45 minutes with an engineer from the team, and the first 20 minutes are a deep dive into one project from your past work. You present the project, and the interviewer asks about:

  • the trade-offs you made,
  • the scale the system operated at,
  • the challenges you faced,
  • the hardest part of the project.

Choose a project and be ready to go into detail on each of these.

Clarifying Questions

  • Should I start with a short overview and let you steer, or go straight to specific areas?
  • How deep should I go: architecture level, or down to code and data structures?
  • Does the project need to be recent, and is it fine if parts of it were owned by other teams?

Hints

Hint 1

Pick for depth: Choose a project where you made or shaped the key decisions yourself, so that you can answer two or three levels of "why" about each one.

Hint 2

Bring real numbers: Scale questions go better with figures you actually know about the system, such as traffic, data size, latency targets and team size, than with adjectives like "large".

Follow-up questions

  • If load grew tenfold, which component would fail first, and what would you change?
  • Which decision would you reverse with hindsight, and what did it cost the project?
  • How did you measure whether the project succeeded?
  • Which parts did you not own, and how did you work with the people who did?