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Kahaan: building a Kolkata guide from an everyday question

How an everyday question led me to build a multilingual Kolkata guide for toilets, bins and e-waste destinations with AWS.

Sayan

I’m from a village, and this idea started with something ordinary: watching people struggle to find a toilet, a bin, or somewhere to take old electronics. I kept coming back to one question — kahaan? Where?
For Environmental Hacks, I turned that question into a small Kolkata pilot. Kahaan lets people browse toilets and bins, or search an item like a charger, read disposal guidance and check a listed destination before opening directions. The interface supports English, Bengali and Hindi. Browsing is open; adding, confirming or reporting a place requires sign-in.
The hardest part was the data. An address on the internet doesn’t automatically mean a public drop-off point. I chose to keep sources and uncertainty visible. The pilot has 31 online-sourced listings, mostly toilets. Waste coverage is still small. For batteries, it shows no suitable destination because acceptance hasn’t been established.
AWS supports the shared contribution system. Amplify hosts the app, Cognito handles sign-in, and API Gateway and Lambda protect and validate contributions. DynamoDB stores places and votes. A conditional transaction records each account’s vote and updates the counter together, preventing duplicate votes from increasing it. Creators cannot vote on their own places.
I used Codex to help with coding, research and UI refinement, while choosing the problem and reviewing the product. The biggest lesson was that a useful app needs honest answers, including when it doesn’t know.
This is an early pilot, with no field checks or measured environmental impact yet. Next, I’d focus on better acceptance evidence and moderation. The code is open for others to explore and contribute.
Try Kahaan:  https://demo.dato5zt1h00lk.amplifyapp.com  Source code:  https://github.com/sayan365/kahaan  Demo video:  https://youtu.be/jcpuXHB0zng 
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