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Junior Software Engineer interview questionsSystem Design round
A 60 min interview plan with a time-boxed script, what each question is for, and the signals to score against. Key skills: Designing scalable and efficient software systems..
System Design Challenge
Design a basic chat application that allows users to send text messages to each other in real-time. Follow-Up Questions: How would you handle multiple users and ensure messages are delivered promptly? What database would you choose to store messages, and why? How would you scale the application to handle a growing number of users?
What this question is for, and what to listen for
Purpose
Assess ability to design simple systems, understanding of real-time communication, scalability considerations, and use of appropriate technologies.
Signals to score
- Understands the core components required
- Identifies the need for a client-server architecture
- Discusses use of WebSockets or similar for real-time communication
- Considers user authentication and message storage
- Addresses scalability concerns
- Explains choice of database
- Demonstrates understanding of load balancing
- Thinks about fault tolerance
- Communicates ideas clearly
Follow-up questions
- Can you outline the main components you would need for this application?
- How would you manage real-time message delivery between users?
- What challenges might arise with increasing user numbers, and how would you address them?
- How would you ensure data consistency and reliability?
If you had more time, what improvements or additional features would you consider adding to your design?
What this question is for, and what to listen for
Purpose
Assess the candidate's ability to think beyond basic requirements and consider enhancements or optimizations.
Signals to score
- Suggests additional features like group chats or media sharing
- Considers implementing message encryption for security
- Thinks about user presence indicators
- Discusses potential for push notifications
- Considers UI/UX improvements
- Reflects on performance optimizations
- Shows interest in continuous improvement
Great job on the system design exercise!
What this section is for
Purpose
Provides positive reinforcement to the candidate, helping to build confidence and create a supportive atmosphere before moving into the final part of the interview.
Closing
What this section is for
Purpose
Thank the candidate for their time, provide next steps, and leave a positive final impression.
Do you have any questions for me about the team or the company?
What this question is for, and what to listen for
Purpose
Gauge the candidate’s curiosity and interest in the role.
Signals to score
- Asks thoughtful questions about the team or company
- Shows interest in company culture
- Inquires about technologies used
- Expresses curiosity about learning opportunities
- Asks about next steps in the process
- Engages actively in the conversation
- Demonstrates enthusiasm for the role
Follow-up questions
- Is there anything else you'd like to know about the projects we work on?
- Do you have any questions about how our team operates?
Junior Software Engineer interviews — common questions
- Who is this Junior Software Engineer interview plan for?
- It is written for the interviewer, not the candidate: the hiring manager, engineer or panel member running the System Design round for a Junior Software Engineer role. It gives you a 60 min script to follow in the conversation — 3 questions with what each one is for and the signals to score against — so you are not writing the round from scratch the night before.
- What does the System Design round assess?
- This round is focused on: Designing scalable and efficient software systems.. It works through System Design Challenge and Closing, scoring against 23 observable signals, with follow-up prompts on 2 of the 3 questions for going deeper where an answer is thin.
- How is the 60 min split up?
- System Design Challenge (45 min), Closing (10 min). The timings are there so the round stays on schedule and every candidate gets the same shape of interview — which is what makes two candidates comparable afterwards.
- What other rounds should I run for a Junior Software Engineer?
A single round does not cover a whole role. The other rounds in this library for a Junior Software Engineer: