Introduction to the System Design Interview

System design interviews may seem strictly focused on assessing your technical abilities, but that’s not quite the case.

System design vs. coding interviews

The system design interview is categorized as a technical interview, much like a coding interview, but it differs significantly. For example:

• Most prompts are intentionally vague. Coding challenges are clear; system design prompts are not. The system design interview mimics real-world conditions, so the interviewer doesn’t give you clear requests with features neatly outlined. Mostly, you have to tease out specifics yourself, which is why asking clarifying questions and following a framework are so important.
• There is no "right" answer. It's true that there are good designs and bad designs, but as long as your choices are justifiable and you articulate tradeoffs, you should let your creativity shine.
• You're engaged in a two-way dialogue. This is critical. In a real-world scenario, you wouldn't go off on your own with only a vague idea of what to build. You want to work with your interviewer every step of the way. Clarify requirements in the beginning, check in throughout, and evaluate your choices at the end.

Even the most brilliant engineer can tank the system design interview if they forget that communication skills are being assessed too. The best engineers ask a lot of questions, think through tradeoffs, and justify their choices to build a working system.

What to expect

Typically, the system design interview lasts 45-minutes to an hour, including time for introductions and Q&As from the interviewer. However, companies such as Amazon could mix a system design question with behavioral questions, or even conduct 20-minute system design interviews.

You'll be asked to use the whiteboard (if you're in person) or an online tool such as Google Drawings, Whimsical, or Miro to outline your design.

Companies take various approaches when selecting interview questions. Some like to ask you to design systems that will solve problems they're actually facing. Others avoid these questions, because it may introduce a bias for interviewers to favor solutions that mirror their actual systems.

Regardless, a system design question is broad enough so that there isn’t only one “correct” answer, but includes sufficient context so that you can give a more focused solution. The question is presented in a broad form initially (e.g. Design TikTok), and it’s up to you to narrow the problem scope.

Oftentimes, the interviewer tailors the expectations and guardrails of the question based on your experience level. For mid-level engineers, certain constraints and requirements are given to narrow the scope and complexity of the problem. In contrast, senior-level engineers are expected to navigate a more ambiguous problem statement with a broader scope and weigh tradeoffs based on a deeper understanding of system design principles.

What interviewers are looking for

Interviewers don’t expect you to create a 100% perfect solution. Instead, the interviewer assesses how well you:

• Clarify ambiguity around system and/or product requirements
• Navigate a complex problem by considering constraints, bottlenecks, and tradeoffs
• Discuss and evaluate multiple solutions, weighing the pros and cons of each to reach a workable solution
• Identify scaling opportunities, potential risks, and/or points of failure

For an in-depth look into how interviewers assess candidates, review our Rubric for System Design Interviews.

How to prepare for a successful system design interview

You can best prepare for the interview by ensuring you have a solid grasp on:

1. An interview framework to organize your solution and communicate it effectively with the interviewer.
2. System design principles to guide your decisions when weighing complex design tradeoffs.
3. Practicing with real-world system design questions, which helps you apply your knowledge to real-world interview questions. We recommend watching Exponent’s mock interview videos to see hands-on examples of different answer approaches.