Getting into Kendall Ford in Bozeman is basically impossible. I’m not exaggerating—scheduling anything is a multi-month endeavor. My 2021 F-150 is still under powertrain warranty, which means I’m supposed to care about documented service intervals, but the dealership has made that inconvenient enough that I’ve just embraced doing it myself.
I service everything at home anyway—the F-150, some ATVs, a mower, a snowblower. Once you have the tools and some confidence, DIY is usually faster, cheaper, and less painful than the alternative. The problem is keeping track of all of it.
The real issue with the F-150 specifically is the warranty. If something goes sideways with the drivetrain, I need receipts. I need documented oil changes at the right intervals. I needed somewhere to log this stuff that wasn’t a stack of folded-up receipts in the glovebox.
So I built Wrenchtron.
The Problem
Nothing out there handles a mixed fleet well. Apps designed for “car guys” are overkill and assume you’re running a shop. Generic spreadsheets are fine until you have five vehicles with different maintenance schedules. OBD-based apps only work while you’re plugged in and don’t help with the mower.
I also wanted receipt capture. I’m running Kirkland 5W-30 and buying OEM filters at the dealership parts counter—best of both worlds, keeps the warranty happy. I want that receipt for the filter and the Costco run attached to the log entry. That’s the documentation that makes the warranty coverage real.
The Solution
Wrenchtron tracks service history across your whole fleet—whatever that looks like. It handles photos, receipts, costs, and maintenance schedules, and it works offline. You can install it on your phone like a native app.
Features that matter:
- Five interval types — mileage, time (months), seasonal, calendar month, and composite (whichever comes first). An oil change might be 5,000 miles or 6 months; Wrenchtron tracks both and alerts on whichever triggers first
- Maintenance Hub — cross-fleet overview of what’s overdue, what’s due soon, and what’s coming up. One screen to see if anything needs attention across all your vehicles
- Projected mileage — enter your annual mileage rate and it estimates when you’ll hit the next service threshold, so you can plan ahead instead of react
- NHTSA recall integration — auto-fetches open safety recalls by VIN so you don’t have to remember to check
- Receipt photos — attach images to any service log entry; Firebase Storage handles the uploads
- Typed service records — oil changes track oil weight, brand, and filter; tire services track position, size, and tread; brakes track pad type and whether rotors were replaced. Structured data, not freeform notes
- PWA with offline support — installs on iOS/Android, Firestore syncs via IndexedDB so the data is there even without a connection
- Cost tracking — every service log has an optional cost field; stored in cents internally so there’s no floating point nonsense
The Stack
Next.js 15 static export, Tailwind CSS v4, Firebase for auth, Firestore, and Storage, with @serwist/next handling the PWA layer. Hosted on Firebase Hosting. No server, no API routes—everything runs in the browser and security is enforced entirely by Firestore and Storage rules.
Firebase as the Backend
The whole app is user-scoped in Firestore under users/{userId}/vehicles/{vehicleId}, with maintenance logs as subcollections. Security rules check request.auth.uid == userId on every read and write—there’s no server middleware to forget, and it’s hard to get wrong.
Firebase Authentication uses Google sign-in only. One button, no password reset flows, no email verification. I don’t want to manage credentials.
Cloud Storage handles vehicle photos and receipt images. Uploads go through browser-image-compression before hitting the API so nobody’s syncing uncompressed phone photos into my storage bucket.
Firebase Hosting deploys the static export. GitHub Actions runs Vitest on push, and if tests pass, it builds and deploys to Firebase. The whole pipeline is a few minutes.
The Maintenance Logic
The service interval engine lives in src/utils/maintenance.ts—pure TypeScript, no React, no Firebase. It takes a vehicle and its service history and calculates alert status for every maintenance item: overdue, due soon, or fine.
Keeping it framework-free was intentional. It’s easy to test with Vitest, easy to reason about, and easy to swap out if the rest of the app changes around it. The projected mileage calculation is in there too—given an annual mileage rate and last known odometer, it estimates when the next mileage-based service will hit.
Check it out
Live: https://wrenchtron.com
Demo (no login): https://wrenchtron.com/demo
Source: https://github.com/swantron/wrenchtron
If you’re doing your own work and need somewhere to log it, give it a shot. If you’re waiting three months to get into a dealership, maybe just do the oil change yourself and log it here.
40%-ish solar eclipse in Bozeman. Time to make crescents.