Common System Design Prompts (and what they test)

This is a “why this question” map so you can practice deliberately.

URL shortener

Tests:

• API design and data modeling
• capacity planning basics
• caching and TTL

Rate limiter

Tests:

• algorithms (token bucket/leaky bucket)
• distributed coordination tradeoffs
• hot keys and performance

Notification system

Tests:

• async processing
• retries, DLQs
• user preferences, idempotency

Feed / timeline

Tests:

• fanout tradeoffs (push vs pull)
• storage and caching
• consistency and freshness

File upload / media processing

Tests:

• object storage patterns
• async processing pipelines
• security and abuse prevention