Just went through the Yelp senior SWE loop and the system design round was probably the part I prepared least for and it showed. Writing this for anyone searching before they start.
The prompt I got was roughly: design the Yelp search backend. Which, yes, they literally asked you to design Yelp at Yelp. At first I thought it was a trap but the interviewer was genuinely interested in the depth of my reasoning, not gotcha moments.
What they actually care about: Ranking and relevance. They sell local search, so if you don't bring up ranking signals early (proximity, rating score, review recency, categorical filters), the conversation goes sideways. Read vs. write separation. They pushed hard on how I'd handle the write path for review ingestion vs. low-latency reads. Know your caching strategies, and have something to say about eventual consistency vs. strong consistency trade-offs. Geo-indexing. This came up naturally: how do you handle queries that are location-bound? I talked through geohashing and they seemed satisfied. You don't need to go deep on the math, just show you know it exists.
Format: 45 minutes, one interviewer. First 5-10 minutes they confirmed the scope with me. Then I drove. They interrupted a few times with "what if the load is 10x" type questions, classic.
Level calibration: At L5, they're not just checking if you can draw boxes. They want to see you make decisions and defend them when challenged. I got pushed back twice and both times it was really them checking if I'd fold under pressure. Once I held my ground with reasoning, the temperature dropped.
For prep: designing for search and ranking is different from your typical rate limiter or URL shortener prompt. If your design doesn't have anything to say about result relevance, you'll probably miss the mark here specifically.
Happy to answer questions. Loop was 5 rounds total, this was round 3.