1. Design a URL Shortener

The brief

Design a URL shortener that creates links and redirects visitors to their original destination. Define the create and redirect contracts, how short codes remain unique, and how expiry and deletion affect cached redirects. Explain one failure from the visitor’s perspective.

• Create 1 million links/day; each link receives 100 redirects on average.
• Redirect traffic peaks at ten times the daily average. Store the destination and owner for one year.
• Owners may expire or delete a link. Custom aliases and detailed analytics are optional follow-ups.

Constraints

Redirect latency≤ 100 milliseconds

State a p95 server response target, excluding the destination website and internet transit.

Unique destinations

Concurrent creates and retries must not assign one short code to two different destinations.

Deletion and expiry

State a bounded delay for invalidating redirects and how clients see expired or deleted links.

What to cover

1. 01

   API and data model

   Define link creation, redirect and deletion responses, identifiers and ownership.

2. 02

   Read and write paths

   Show durable link storage, code allocation and the redirect cache.

3. 03

   Capacity estimate

   Estimate average and peak redirect QPS and one year of storage with stated record size.

4. 04

   Failure and tradeoff

   Trace a duplicate create and a cache outage; compare two ways to allocate codes.

Worked designs

Explore the architecture and decisions, then build on an example with Coach.

Official design

Design a URL Shortener like Bitly

Seven-character codes that never clash, a billion redirects a day from three layers of cache, takedowns everywhere within a minute: one-hour boards for junior, senior and staff, with the theory behind them.

Explore the design

Review rubric

AI feedback uses these criteria. Scores are practice feedback.