What "private" means here — and how to check it
"We delete your files after 24 hours" is a policy. "Your files are never transmitted" is an architecture. These tools are the second kind: decoding, converting and packaging all happen in your browser's own engine and WebAssembly, so there is no server copy to delete, leak, subpoena or train on. The How it works page walks through verifying this with your browser's developer tools in under a minute — the site works with your connection switched off after loading.
Three honest boundaries: the page itself is served by a host (Cloudflare) that sees ordinary web-traffic metadata, like any website; a cookie-less performance beacon reports page-load timing (never file data); and if advertising appears on some pages in the future, ad scripts will be kept out of reach of the file inputs — the privacy policy spells all of this out in plain language.