Designing a URL shortener (like bit.ly or TinyURL) is one of the most popular system design interview questions—and for good reason. It’s simple enough to explain in a minute but complex enough to explore deep system design concepts.
This seemingly simple service—taking a long URL and returning a short one—touches on databases, caching, scalability, API design, and more. It’s the perfect introduction to practical system design.
What You’ll Learn
In this comprehensive case study, we’ll design a complete URL shortening service from scratch:
- Requirements gathering: Functional and non-functional requirements
- Capacity estimation: How much data? How many requests?
- API design: Clean, RESTful endpoints
- URL encoding: Base62, hashing, or auto-increment IDs?
- Database schema: Choosing between SQL and NoSQL
- Caching strategy: Reducing database load for popular URLs
- Analytics: Tracking clicks and gathering insights
- Scalability: Handling millions of URLs and billions of redirects
- High availability: What happens when components fail?
Why This Design Matters
URL shorteners might seem trivial, but they involve many classic system design challenges:
- Unique ID generation: How do you generate short, unique identifiers at scale?
- Read-heavy workload: Far more redirects than URL creations
- Low latency requirements: Every millisecond counts for redirects
- Data persistence: URLs must never be lost
- Analytics at scale: Tracking billions of clicks without slowing redirects
Solving these challenges teaches you patterns applicable to many other systems.
Real-World Applications
The techniques you’ll learn apply far beyond URL shorteners:
- Unique ID generation is needed for user IDs, order IDs, and more
- Read-heavy optimisation applies to social media feeds, product catalogues
- Fast redirects are similar to serving static content at scale
By the end of this case study, you’ll have designed a production-ready system and learnt patterns you can apply to countless other design problems.
Let’s build a URL shortener!