WebApp Shell

A tiny, offline-first PWA shell that renders self-contained HTML pages encoded directly into the URL. It's a successor to opening data:text/html;base64,… URLs from iOS Shortcuts — but on a real, persistent origin.

Live: https://appshr.github.io/webapp-shell/

What it does

1. Open the shell. Paste a self-contained HTML page into the builder.
2. It encodes your HTML (base64url, optionally gzip-compressed) into a link like:

   https://appshr.github.io/webapp-shell/#app=<base64url>
   https://appshr.github.io/webapp-shell/#appz=<gzip+base64url>
   

3. Opening that link renders your page full-screen inside the shell.

Why it beats raw data: URLs

	data: URL	WebApp Shell
Runs offline	yes	yes (service worker)
Persistent localStorage / IndexedDB	❌ opaque origin	✅ real origin, survives launches
Add to Home Screen (full-screen)	❌	✅
Stable, shareable URL	❌	✅

The payload lives in the URL hash (#), on purpose

• The hash is never sent to GitHub's servers, so there are no URL-length or routing limits, and the service worker always matches the cached shell — meaning any generated link works fully offline after the first load.
• Encoding is base64url (-/_, no padding) so it's URL-safe everywhere.
• With gzip (Safari 16.4+) the link stays much shorter.

Using it from Shortcuts

1. Generate a link in the builder and Copy it.
2. Add an “Open URLs” action in Shortcuts and paste the link.
3. Running the shortcut opens your app in Safari — offline, with its data intact.

Shortcuts opens URLs in Safari (with its minimal toolbar). iOS does not allow Shortcuts to launch directly into a chrome-free standalone window — that's an OS limitation, not something a web page can change.

True full-screen (no Safari chrome)

1. Open your app link, then in Safari tap Share → Add to Home Screen → Add.
2. The icon launches your app full-screen, offline, with its own storage.

The shell auto-injects apple-mobile-web-app-capable and a viewport meta if your page is missing them, so any pasted page becomes full-screen-capable.

Why not webapp://?

Custom URL schemes can only be claimed by native apps on iOS (via Info.plist). A web page / PWA cannot register webapp://, so it can never be launched that way. The https:// links this tool generates do everything that scheme was meant to do.

Offline guarantee

The first online load caches the shell permanently via a service worker. After that the shell and every link work with no network. Your app only needs the internet if its own code fetches something external — keep pages self-contained to stay 100% offline.

⚠️ Security note

Anything you load runs on the appshr.github.io origin with full access to its storage. Only open links you created or trust: a malicious page could read or wipe the data of your other shell apps.

Files

• index.html — the shell (renderer + builder UI)
• sw.js — service worker (offline cache)
• manifest.webmanifest — PWA manifest
• icon.svg, icon-192.png, icon-512.png — icons