URL Shortener

Overview

Create a Bit.ly-style service. Users submit a long URL, get a short link, and see real-time click analytics (total clicks, clicks by country/device/referrer, click timeline chart). Build the backend API, redirect service, and analytics dashboard.

The URL shortener is the single most frequently asked system design interview question, and actually building one demonstrates that you understand the topic at a depth that whiteboard discussions alone cannot convey. You will implement a short code generation strategy, design a database schema for URLs and click events, build a Redis caching layer for fast redirects, and create an analytics dashboard that aggregates click data across multiple dimensions.

The engineering challenges are surprisingly rich. The redirect endpoint must be extremely fast (every millisecond of latency costs user trust) so you need Redis cache-aside with PostgreSQL fallback. Click tracking must be asynchronous to avoid blocking the redirect response. Short code generation must handle collisions without degrading performance. Rate limiting prevents abuse while keeping the API responsive for legitimate users.

For interviews, this project is a goldmine. You can walk through the system design with concrete implementation details: cache hit ratios, database indexing strategies, the trade-off between Base62 encoding and random codes, async event processing, and time-series analytics aggregation. Having working code transforms a theoretical system design answer into a credible engineering discussion.

Interview questions

• How do I generate short codes?
• How should I handle redirects efficiently?
• What analytics should I track?
• How do I implement rate limiting?
• What database schema should I use?
• How do I handle URL validation and security?

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