Interview format

System Design

Overview

Perplexity’s System Design interviews are technical exercises that require candidates to design a system under various constraints, requirements, and ambiguities.

Logistics

System design interviews are typically 45 to 60 minutes in length, conducted live with either one or two interviewers. You’ll have access to a physical or virtual whiteboard.

Question format

Our system design questions are open-ended exercises that require candidates to design and/or refine a system under various constraints, requirements, and ambiguities. The question will cover one or more technical domains relevant to Perplexity, and there is no single correct solution.

Typically, the premise will be stated by your interviewer, and you’ll collaboratively fill in additional details over the course of the interview. Some system design questions involve documentation that will be provided to you at the time of the interview.

Evaluation criteria

We evaluate system design interviews along several dimensions, including but not limited to:

• Problem framing: how well do you develop a clear and intuitive understanding of the situation?
• Requirements: do you efficiently identify and prioritize the requirements of the system? How sharply do you focus on the problem’s high-order bits?
• Core architecture: how sound is the core architecture you propose? Do you fit the architecture to the problem, or do you try to fit the problem to a prememorized template?
• Scaling and bottlenecks: how well do you reason quantitatively about issues of scale, and what starts breaking with successive orders of magnitude of scale?
• Identifying and navigating tradeoffs: can you identify the most important tradeoffs in the system, and do you navigate them with good judgment and clear thinking?
• Adaptability: how flexibly can you react to new information and changing requirements?
• Domain expertise: for questions that touch on a specific technical domain, what degree of expertise do you demonstrate in that domain? Can you translate that expertise into sound solutions to the problem at hand?

Tips

Covering the full scope of a system design question is not required (and not really possible). There is no way to explore all the contours of even a moderately large-scale system in an hour. In fact, if you feel you’ve covered everything worth covering, you’ve probably missed some crucial aspects or explored them in insufficient depth. You’ll need to be selective in what you choose to zoom in on. Develop a good sense of the important details to flesh out versus the routine plumbing that you can skip over.

Complexity ≠ quality. There is a common misperception that system design interviews are about invoking as many fancy concepts as possible to showcase the breadth of a candidate’s knowledge. This often leads to solutions that are gratuitously complex. While we do care about your breadth of knowledge, we care more about whether you’re able to apply that knowledge in sound, high-judgment ways. Similarly, avoid overfocusing on the precise details of systems you’ve worked on in the past.

Remember your interviewer’s perspective. Your interviewer is thinking about what it might be like to collaborate with you on designing the next generation of Perplexity’s systems. They will appreciate clear and methodical communication, along with well-calibrated statements of confidence in any given idea or approach.