Cowin Appointment Listener

During India's COVID-19 vaccination drive, millions of people were competing for a handful of appointment slots on the CoWIN portal. Slots would appear and disappear within seconds. I built a tool that monitors the CoWIN API continuously and alerts you the moment a slot opens in your area -- so you can actually book one before it vanishes.

The Challenge

The CoWIN public API had rate limits and returned data organized by district and date. I needed to poll efficiently without getting blocked, parse the nested response structure quickly, and alert users instantly -- seconds mattered when slots disappeared in under a minute.

How I Built It

This is a pure frontend React app -- no backend needed. The user selects their state and city, and the app starts polling the CoWIN API at regular intervals directly from the browser. When it detects available slots matching the user's criteria, it fires a sound alert immediately. I kept the architecture deliberately simple because speed of deployment mattered more than elegance -- people needed this tool now, not after a two-week sprint.

Impact

I built and shipped this in under a month while the vaccination crisis was at its peak. It helped friends and family secure appointments they'd been trying to book for weeks. This was a lesson in building for urgency -- scoping ruthlessly, shipping fast, and solving a real problem for real people when it mattered most.