What software engineer interviews actually test
Software engineering interviews at most companies follow a predictable structure — once you understand the components, preparation becomes systematic.
Coding (DSA — data structures and algorithms):
The most discussed part of the process. Expect 1–3 rounds of live coding on a platform like LeetCode or CodeSignal. Focus on arrays, strings, trees, graphs, dynamic programming, and sliding window patterns. The goal is demonstrating problem-solving process as much as correct answers.
System design:
For mid to senior roles: design a scalable system (URL shortener, social media feed, ride-sharing backend). You're being tested on your knowledge of databases, caching, load balancing, APIs, and trade-offs between consistency and availability.
Behavioural:
Every company does this — FAANG more than most. The goal is to surface how you collaborate, handle conflict, take ownership, and deal with failure. Prepare 5–6 strong stories from your experience that can be adapted to different questions.
Technical depth:
Questions about your specific technology stack: language features, concurrency, memory management, testing practices, and debugging approaches.
The format at large vs. small companies:
FAANG and large tech companies run structured 5–7 round loops with DSA and system design as mandatory components. Startups often skip DSA in favour of practical take-home exercises or pairing sessions on real codebase problems. Know which type you're interviewing for.
Behavioural software engineer interview questions
"Tell me about the most technically challenging project you've worked on."
Lead with the complexity, not the technology. What made it hard — scale, ambiguity, tight timeline, novel problem? What was your specific contribution? What did you learn? Quantify the outcome if you can.
"Describe a time you disagreed with a technical decision. What did you do?"
What they're evaluating: whether you can advocate for your position with data while remaining collaborative. The right answer includes: how you raised your concern (privately before publicly), what evidence you presented, and how you responded when the decision went against you.
"Tell me about a time you had to debug a difficult production issue."
Structure: what was the symptom, how did you isolate the cause, what was the root cause, what was the fix, and what did you put in place to prevent recurrence? Show systematic diagnosis, not luck.
"How do you handle technical debt?"
Interviewers want to see pragmatism. Good engineers acknowledge trade-offs: sometimes shipping matters more than perfect code. Show that you document technical debt explicitly, advocate for addressing it during planning, and prioritise it against feature work — rather than pretending it doesn't exist or refusing to ship until code is perfect.
"Tell me about a time you mentored a junior engineer or helped a teammate grow."
This matters increasingly as you move from junior to senior. Show specific actions: code reviews with explanations not just corrections, pairing sessions, creating documentation, or giving a teammate ownership of a feature to help them develop.
"How do you keep your technical skills current?"
Be specific: side projects, open source contributions, reading engineering blogs (particular favourites), conference talks, or internal learning. Avoid vague answers like "I just keep up with the industry."
Technical and system design interview questions
"What is the difference between REST and GraphQL?"
REST: fixed endpoints that return predefined data shapes; simple, widely understood, good for standard CRUD operations. GraphQL: single endpoint where the client specifies exactly what data it needs; reduces over-fetching and under-fetching, but adds complexity. Trade-off: REST is simpler to cache and reason about; GraphQL is more flexible for complex, nested data needs.
"How would you design a URL shortening service like bit.ly?"
Cover: API design (POST to create, GET to redirect), database schema (original URL, short code, metadata), hash generation strategy (random vs. sequential, collision handling), read vs. write load characteristics (reads dominate), caching strategy (Redis for hot URLs), and scalability considerations. Show you think in systems, not just code.
"What is the difference between a process and a thread?"
A process is an independent program with its own memory space. Threads share memory within a process. Threads are cheaper to create and switch between but require careful synchronisation. Follow-up: describe a race condition and how you would prevent it.
"How would you approach testing a new feature?"
Cover levels: unit tests (isolated functions), integration tests (components working together), and end-to-end tests (full user flows). Mention test coverage thresholds, CI pipeline integration, and the trade-off between test coverage and maintenance cost. Bonus: mention TDD if you practise it, but don't claim to if you don't.
"What happens when you type a URL in a browser and press enter?"
Classic depth question. Walk through: DNS resolution, TCP handshake, TLS negotiation (for HTTPS), HTTP request, server processing, response, and browser rendering. Go as deep as you know — the interviewer will follow up if they want more.
Questions to ask — and how to prepare with LoopCV
Questions to ask your interviewer:
- What does the on-call and incident response process look like?
- How is technical debt prioritised against new feature work?
- What does the code review process look like here?
- How autonomous are engineers in choosing their technical approach?
- What does the path from senior to staff engineer look like at this company?
How to prepare:
For DSA: LeetCode medium-difficulty problems are the target for most interviews. Solve 50–100 problems systematically across topics rather than grinding random problems. Practise explaining your approach out loud — interviewers follow your thinking, not just your code.
For system design: read "Designing Data-Intensive Applications" (Kleppmann) and practise drawing architectures on a whiteboard or shared screen. Practise talking through trade-offs, not just describing components.
Use LoopCV's interview preparation tool to rehearse your behavioural answers and practice system design walkthroughs before the interview — getting the verbal flow right under pressure is a skill in itself.
On the applications side: many SWE roles receive hundreds of applications. LoopCV applies automatically to matching roles every day, keeping your pipeline active while you're in interview prep mode.