HardExperience level: 8-15 years1 min read

How would you design a URL shortener like bit.ly?

Reviewed by Gurusankar M.

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Concept Made Simple

Coffee Chat Question

“How would you design a URL shortener like bit.ly?”

Remember It Faster

Mind Map Answer

Core job: map a short code to a long URL, then redirect. The interesting parts are the key generation and the read-heavy scale.

Write
Generate unique short code → store mapping
Read
Look up code → 301 redirect
Scale
Cache hot links, read replicas, CDN
Keys
Base62 of an ID counter, or hash + collision check

Think Beyond the Expected

What If?

How do you guarantee short codes are unique without a central bottleneck?

Pre-allocate ranges of IDs to each app server (a key-generation service hands out blocks), or use a distributed counter like a ZooKeeper/Snowflake-style ID. Each server then Base62-encodes from its own range — no contention.

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Plain-language foundations

I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner.

Topic: Scaling (System Design)
Interview question: "How would you design a URL shortener like bit.ly?"

Please:
1. Explain the core idea in simple, plain language, using an everyday analogy.
2. Define any technical terms you use.
3. Walk through one small, concrete example.
4. Finish with a single sentence I can easily remember.

Keep the tone friendly and assume I'm new to this topic.
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