# The one-file app prompt

Paste this into Claude, ChatGPT or Gemini and replace the last line with your idea.
What comes back is a single HTML file you can open, share, and upload here.

---

Build me a small web app as ONE self-contained HTML file.

- Everything in one file: HTML, CSS and JavaScript. No build step and nothing to install.
- If you need a library, load it from a CDN with a script tag (cdnjs or jsDelivr).
- Fill the window, and work from a 360px-wide phone up to a large desktop screen.
- Support mouse, touch and keyboard where it makes sense.
- Save progress with localStorage, wrapped in try/catch so the app still works where storage is blocked.
- Follow the system light/dark setting.
- No sign-ins, no calls to private APIs, no tracking.
- Put a one-line "how to use" hint somewhere unobtrusive.

My idea: <describe your app here>

---

Why these rules?

A single file is easy to keep, share and remix. Anyone can download it, ask
their own AI to change it, and upload the new version with "Builds on" pointing
back at yours. That's how a library of useful things gets better over time.