My 8-Year-Old Built the F1 Reaction Test Every Website Gets Wrong

Every "F1 lights reaction tester" on the internet is broken. Not buggy — just wrong about what F1 drivers actually do.

You know the drill. Five red lights come on. They go out. You click as fast as you can. Some site tells you your reaction was 230ms and to try again.

That isn't what F1 drivers do.

A real driver sits at the grid with the clutch already pulled in. When the lights go out, they release the clutch. The reaction isn't a click — it's a release.

My 8-year-old noticed this. He watches every race. He kept asking why none of the online ones felt right. So he opened Shelf and typed:

> "F1 start lights reaction test. Hold spacebar before lights, release when they go out. Show reaction time."

12 seconds later he had it. Working. On his laptop. Forever.

## Why no website builds this

It's not hard to build. It's hard to justify building.

A solo dev wanting to ship a "reaction time" tool picks the click version because:

- 95% of visitors don't know about the clutch thing

- Adding a hold-to-release mode adds settings, edge cases, mobile fallback

- Every extra feature is one more thing to maintain for the next 10 years

- There's no money in F1 reaction testers anyway

So you get the same generic version everywhere. The 5% with a specific need — kids who watch races, sim racers, motorsport fans — get nothing.

This is the customisation tax. Every piece of software you use is a compromise between what you want and what was profitable to ship to a million people who mostly want the same thing.

## What changed

The economics changed. The cost of a one-person tool used to be "learn to code, spin up a server, host it, maintain it." Now the cost is one sentence in plain English.

That's what Shelf does. You describe a tool — even a weird, hyper-specific one only you and your kid care about — and it builds it as a real app on your machine. SQLite-backed. Offline. Forever. No account, no hosting, no JS framework to learn.

It scales the other way too. The same prompt mechanism that made my kid's reaction tester also makes:

- A patient handover form for a nurse

- A daily P&L tracker for a small shop

- A revision quiz scoped to one chapter of one textbook

- A 5-minute classroom timer with the exact sound that teacher likes

Every one of these is a real tool somebody needs. None of them are big enough for a startup to build. All of them are 30 seconds of typing in Shelf.

## Try the F1 reaction tester

I exported my kid's app as a .shelf file. Download it, install Shelf, drag the file into the sidebar — that's the import. His exact app, including the spacebar-release mechanic, runs on your machine.

- Download Shelf: [shelf.app](https://shelf.app)

- Download the F1 reaction tester: [f1-reacting-lights.shelf](https://raw.githubusercontent.com/soyu-apps/getmyshelf.app/refs/heads/main/samples/f1-reacting-lights.shelf) (attach when posting)

- Or build your own: open Shelf and type "F1 start lights reaction test, hold spacebar before lights, release when they go out, show reaction time"

Show it to your kid. See if they can beat his time.

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Shelf is a free desktop app. Data stays on your machine. The point isn't to replace big software — it's to fill the gap big software was never going to fill.