Unit Converter app template

Convert length, weight, temperature, speed and more.

ProductivityWorks offline1 phone feature

This is the template running live. Phone features such as the camera, vibration and notifications work in the app you build.

Phone features this template uses

These come from the FreeApp JavaScript bridge that every app built with Free HTML to APK includes. In a normal browser the template still runs, and the calls simply do nothing.

Vibration

FreeApp.vibrate()

One-shot buzz (default 50 ms) or an [off, on, off, on…] pattern.

How the template calls them

select.onchange = () => {
  convert();
  if (window.FreeApp) FreeApp.vibrate(10);
};

Make it yours with AI

Copy this prompt into ChatGPT, Gemini or Claude, change the idea to yours, and paste the answer back into the editor. It already explains the app shell and the phone features to the AI.

Show the AI prompt

Build a single-file mobile web app (index.html with inline CSS/JS) for Android WebView.

The app: Unit Converter — a unit converter for length, weight, temperature, speed and more. Convert length, weight, temperature, speed and more.

Requirements:
- Mobile-first, touch-friendly UI (min 44px tap targets), works in portrait, supports light and dark mode.
- Use <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover"> and pad for env(safe-area-inset-*).
- Must work fully offline: no CDN or external scripts, fonts or images; persist data in localStorage.

The page runs inside an Android app that injects a native bridge as window.FreeApp. Available APIs:
- FreeApp.vibrate(ms?: number | number[]): void — one-shot buzz (default 50 ms) or an [off, on, off, on…] pattern

Rules for the bridge:
- Always guard calls with `window.FreeApp &&` (or `if (window.FreeApp) { … }`) and provide a browser fallback so the page also works in a normal browser.
- The bridge may be injected after your script runs: do native setup inside `window.addEventListener('freeappready', …)` and also run it immediately if window.FreeApp already exists.
- Do not use alert/confirm for normal feedback; prefer FreeApp.toast when available.

Return the complete index.html in one code block.

My idea: [DESCRIBE YOUR APP IDEA HERE]

Turn it into an Android app

Tap Edit & build online. The template opens in the online editor.
Change the text, colors and code, then pick an app name, an icon and a package name.
Build. You get a signed APK to install and an AAB for Google Play, free, with no account and no watermark.

✏️ Edit & build online GET IT FREE ONGoogle Play