The ultimate guide to passing system design interviews

System design interviews are a cornerstone of technical hiring processes, assessing your ability to tackle open-ended engineering challenges. To ace these interviews, you need to showcase how you think, communicate, and adapt.

This guide pulls together four key strategies to help you crush your next interview. For a detailed description of each strategy, click the link to the full blog.

1. Stay focused on the problem

System design interviews are intentionally vague, testing your ability to identify the real problem and align with the interviewer’s expectations. Before diving into a solution, clarify the scope, constraints, and priorities.

Key tips:

• Ask clarifying questions. Avoid jumping into solutions prematurely. For example, when designing a social media feed, ask whether you're building from scratch or enhancing an existing feature.
• Avoid overcomplication. Don’t introduce unnecessary complexity to showcase expertise. Instead, focus on foundational aspects and add complexity only when relevant.
• Tailor your approach. Identify the system's bottlenecks and prioritize solving the core issues.

Read more about staying focused on the problem.

2. Communicate effectively

Even with solid technical skills, poor communication can undermine your performance. Clear, structured communication ensures the interviewer understands your thought process and enables collaboration.

Key tips:

• Write it down. Use diagrams or bullet points to explain your ideas. This makes it easier for the interviewer to follow along.
• Explain your choices. Don’t just say, “I’d use NoSQL.” Share why you think it’s the best option based on the problem.
• Keep it moving. If you’re stuck, ask clarifying questions. This shows you’re engaged and thinking through the problem.

Learn how to master communication in system design interviews.

3. Think like an engineer

System design interviews test your ability to think holistically and practically. Success comes from focusing on the user journey, considering trade-offs, and addressing edge cases.

Key tips:

• Focus on the user. Map out the user journey to understand how data flows through the system.
• Don’t stay in hypothesis. Make decisions based on the specific problem you’re solving. For instance, pick a NoSQL database if you’re dealing with fast, frequent updates.
• Plan for edge cases. Think about what could go wrong, like no drivers being available in a ride-sharing app, and how you’d handle it.

Discover how to think like an engineer in system design interviews.

4. Take charge of the design

Show leadership by driving the conversation and focusing on what matters most.

Key tips:

• Start with the problem. Instead of following a rigid checklist, dig into the specific challenges the system faces.
• Tackle the tough parts first. Solve the hardest problems early to show you can handle complexity.
• Present options and trade-offs. Lay out different solutions, explain the pros and cons, and confidently pick one.
• Be flexible. If the interviewer throws new requirements at you, adapt your design without missing a beat.

Learn how to drive the design.

Get holistic interview prep with Formation

The Formation Fellowship gives mid-level and senior engineering job seekers everything they need to land their dream roles—including personalized skill brush-ups, resume help, unlimited mock interviews with experienced software engineers and hiring managers from top-tier tech companies, career and negotiation support, and more. 

If you’re having trouble navigating your job search on your own, apply here and get unconditional support from a team of engineering mentors, technical recruiters, career coaches, and more.