Shop owner vibe-codes an accounting app: one HTML file, 100 test suites, and the rules that keep agents honest
anime_king_1 · reddit · 2026-09-15
A small distribution business owner built his own accounting app with AI agents because nothing off-the-shelf fit: his real unit is a bundle (multiple products, per-item pricing, split invoice lines but merged stock), and some goods are legitimately zero-tax, which every "smart" app kept auto-correcting.
The app is a single HTML file on the shop PC — no login, no internet, no subscription — dozens of versions in, with 100 test suites and tens of thousands of lines of TypeScript, mostly written by agents.
His worst shipped bug: opening via file:// makes Chrome/Edge silently block storage, so a day's entries vanished on tab close. Fixed with a loopback launcher and an undismissable red banner, enforced by a mutation-style test that fails if anyone makes it closable again.
His agent-management rules are the reusable core: never claim something works untested, ask before guessing, never silently remove features; every bug goes into a defect log written from the user's perspective; every new test is mutation-tested; the manual must update in the same commit or the build fails; CI runs on Windows with an end-to-end suite tracking clicks/keystrokes per task.
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