Enter any URL, or a local file:///… path / drag a file in.
Some big sites (Google, Instagram, banks) block being shown in frames — that's their
X-Frame-Options, not a bug; use ↗ Open tab for those.
Local file:// previews only work when you open this tool from your own machine
(the file in ~/mobile-viewer) — the public scalus.app version can't reach your local disk.