Hackathon Workshop — Vibe Coding by Yiyin
I Shipped It. Then I Learned How It Worked.
Building a real product with AI, as a complete backend beginner.
A women in tech nonprofit needed a platform to sell event tickets. Yiyin said yes — a frontend engineer who had never built a backend, never handled payments, never deployed to the cloud. With AI writing most of the code, it shipped: real users, real money.
Then things started breaking.
This is the second of the Herackthon Vibe Coding workshops, and it is the one about what happens after the demo works. Not a case against building this way, but an account of where the gaps open up and what closes them.
Three real bugs from a live system
Each of these came out of a running product, not a tutorial:
- Ticket counts that reset themselves — inventory that did not hold under the conditions a live sale actually creates
- A free event with no capacity limit — the free path skipped the check the paid path enforced, so nothing stopped registrations
- Confirmation emails that fail silently — the send failed, the request succeeded, and nobody found out until someone asked where their ticket was
One of the three is still in production today.
The session walks the real product, the real spec docs, and the code behind each bug, rather than reconstructions of them.
The spec Yiyin did not want to write
The instinct was to start building immediately. A senior engineer insisted on a spec first.
Every one of the three bugs traces back to a question that document did not ask. That is the argument of the workshop: the spec is not process overhead ahead of the fun part, it is where the questions get asked that the code will otherwise answer by accident.
How to interrogate an AI's answer
What to ask before accepting generated code, and why a plausible answer still is not enough. An AI writing code that runs is not the same as an AI writing code that holds — the difference shows up in the cases nobody prompted for.
What you leave with
A one page checklist for your next AI assisted project.
Recorded at the ZILIUDI Herackthon workshop series, Sep 19, 2026. Presented by Yiyin.