Core Cash — core deposit tracker for auto shops
Stop losing money on forgotten core returns.
- role
- Founder, Full Stack Engineer
- duration
- ongoing
- team
- solo
- stack
- Next.js 16 · Supabase · Tailwind v4 · Polar · Resend · Vercel
“the money isn't the problem. forgetting is.”
The problem
Independent auto repair shops pay core deposits — $20 to $300 — on every remanufactured part. Return the old core within 30 days and the money comes back. Miss the window and it’s gone.
Most shops track this on sticky notes. Most shops lose a few hundred dollars a month.
The big shop-management platforms (Tekmetric, ShopMonkey) charge $200-$400/mo and bury core tracking in a submenu three clicks deep.
The approach
One tool. One screen. Log a core in under 30 seconds. Urgency dashboard color-coded by days remaining — green, amber, red, black when overdue. Email reminders at 7/3/1 days out (Pro tier, delivered via Resend on a Vercel cron). Monthly P&L shows deposited vs. recovered vs. written-off, and the recovery-rate percentage.
Industrial-utility aesthetic — warm stone, amber CTA, tabular numerals on every money value, 2px borders. Not generic SaaS.
The stack
Next.js 16 App Router + TypeScript + Tailwind v4 + shadcn/ui on the frontend. Supabase Auth + Postgres with RLS on every table (schema public in git — security from RLS, not obscurity). Polar for billing at $9/mo Pro, because Stripe’s integration overhead was not worth it for a solo-dev niche product.
Reflection
The interesting part wasn’t the tech. It was finding a specific enough wedge: not “shop management”, just core deposits. Ten-thousand of them sit on clipboards every month in the US. I wanted the tool that owned that single action.