Technology · Role guide
Software Engineer Interview Questions & Preparation
Quick answer
A software engineer interview typically runs across a recruiter screen, one or two technical phone screens, and an onsite loop covering coding (data structures and algorithms), system design, and behavioural questions. Expect to write working code, explain trade-offs out loud, and back up your CV projects with specifics.
Overview
Software engineering interviews test three things: can you code cleanly under time pressure, can you design systems that scale, and can you work in a team. The bar rises with seniority — juniors focus on coding fundamentals, while senior and staff candidates spend more time on architecture and influence.
The Software Engineer interview process
| Stage | What to expect |
|---|---|
| Recruiter screen | A 20–30 minute call on your background, motivation and logistics. |
| Technical phone screen | One or two coding problems (arrays, strings, trees, graphs) on a shared editor. |
| Onsite / virtual loop | 2–4 coding rounds, a system design round (mid+), and a behavioural round. |
| Team match & offer | Hiring committee review, team matching, then the offer and negotiation. |
Software Engineer interview questions
These are the questions you're most likely to be asked. Prepare a structured answer for each, and a STAR story for the behavioural ones.
- 1Reverse a linked list and explain your approach.
- 2Design a URL shortener — walk me through the data model and scaling.
- 3Tell me about a time you disagreed with a technical decision.
- 4How would you find the first non-repeating character in a string?
- 5Describe a system you built end to end and the trade-offs you made.
- 6How do you approach debugging a production incident?
- 7Explain the difference between a process and a thread.
- 8Tell me about a time you improved the performance of something.
Example STAR answer
Example answer to: “Tell me about a time you led a technical project under pressure.”
Skills assessed
How to prepare for a Software Engineer interview
- Think out loud — interviewers score your problem-solving process, not just the final answer.
- Clarify the problem and edge cases before you write code.
- Prepare 4–5 STAR stories that show ownership, conflict and impact.
- For system design, start with requirements and scale estimates before drawing boxes.
Common mistakes to avoid
- Jumping into code before clarifying the problem.
- Going silent while you think — the interviewer can't score what they can't hear.
- Memorising answers instead of understanding patterns.
- Ignoring edge cases and testing.
Software Engineer salary
UK software engineers typically earn £45k–£90k, with senior and big-tech roles reaching £120k+ including equity.
Frequently asked questions
How many coding rounds are in a software engineer interview?
Usually 2–4 coding rounds, plus a system design round for mid-level and above and at least one behavioural round.
What's the best way to prepare for a software engineering interview?
Practise data-structure and algorithm patterns out loud, rehearse system design with real requirements, and prepare STAR stories for the behavioural round.
Do I need to know system design as a junior?
Light system design helps, but junior loops focus on coding fundamentals. System design weight increases at mid, senior and staff levels.
Preparing for a Software Engineer interview?
Upload your CV and paste the job description. CareerFast instantly builds your interview readiness score, a company briefing, predicted questions, tailored STAR answers, a mock interview and a downloadable PDF — free to start, no card needed.
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