System Design Interview Questions (Top 25 with Approaches)
The 25 system design questions most often asked at top tech companies, with frameworks for each.
Definition
System design interview questions ask candidates to design a large-scale system (for example: design Twitter, design a URL shortener, design WhatsApp) within 45 to 60 minutes. They test trade-off thinking across scale, latency, consistency, and cost. The frameworks come from the broader system design basics body of knowledge; this article focuses on the actual question set asked at Google, Meta, Amazon, and similar firms.
Why It Matters in Interviews
System design rounds are often the single highest-leverage round in a senior loop: they account for the L5 to L6 decision at Google, the SDE2 to SDE3 decision at Amazon, and similar cuts elsewhere. Per AWS Well-Architected guidance, the same trade-off vocabulary used in production reviews is what interviewers listen for. The 25-question set covers roughly 80% of what gets asked, so pattern coverage beats one-off depth.
How to Use It
Group the 25 into 5 archetypes: feed/timeline (Twitter, Instagram), messaging (WhatsApp, Slack), location-aware (Uber, Yelp), media (YouTube, Netflix), and key-value (URL shortener, S3, Pastebin). Do one full design per archetype, then pivot common variants. Use a 6-step structure: clarify requirements, sketch APIs, estimate scale, draw the data model, draw the architecture, then deep-dive 2 components on demand.
Example
"Design a URL shortener." — Clarify: 100M URLs/day, 100:1 read:write, 7-year retention. APIs: POST /shorten, GET /{short}. Scale: 1.2K writes/sec, 120K reads/sec; 250TB storage over 7 years. Data model: short_code (PK), long_url, user_id, created_at, expires_at. Architecture: write path -> app server -> ID generator (base62 of snowflake) -> SQL primary -> CDC to read replicas. Read path -> CDN -> Redis hot cache (LRU) -> read replica. Deep dive: how the ID generator avoids collisions across regions.
Quick Tips
- Spend the first 8 minutes on requirements and scale estimates; rushing this loses the round.
- Draw on the whiteboard or shared canvas; verbal-only designs are scored lower.
- Name your trade-offs out loud ("I am picking eventual consistency here because reads are 100x writes").
- Reserve 10 minutes for the deep dive; it is the highest-signal section of the interview.
FAQ
Is system design asked for new grads?
Rarely as a standalone round, but the same trade-off thinking shows up inside coding rounds at L4 levels.
How many designs should I prep?
12 to 15 designs covering all 5 archetypes. More than that is diminishing returns.
Should I memorize architectures?
No. Memorize the trade-offs. Architectures vary; the trade-off vocabulary is the constant.