Privacy Policy

Last updated: 2 September 2026

Your audio files

Audio files you drop into mp3tom4b are processed entirely in your browser via WebAssembly. They are never uploaded, transmitted, stored, or shared. The only place they exist outside your device is wherever you choose to save the resulting M4B.

Cover images and metadata

Cover images and the metadata you type (title, author, narrator, year, genre) are also processed only in your browser and end up only in the M4B file you download.

Analytics

We use Vercel Analytics to count anonymous page views. It does not set cookies, does not identify visitors, and never receives any of your audio, metadata, or cover images. No third-party advertising trackers are loaded.

The conversion engine

On your first conversion, your browser downloads the FFmpeg WebAssembly core (about 31 MB) from mp3tom4b's own domain — it is served directly from this site, not from a third-party CDN, and is then cached by your browser for reuse. No data about you or your files is sent in that request.

Optional metadata lookup

If — and only if — you click “Look up online” in the metadata section, the title, author, and narrator you typed are sent to Apple's iTunes Search API (itunes.apple.com), and, when that returns no match, to Open Library (openlibrary.org), to fetch matching book details and cover art. These providers are located outside the EU, including in the United States. This is the only situation in which any text you enter leaves your device; it is strictly opt-in per search, shown to you beforehand, and your audio files and cover images are never involved.

Cookies

mp3tom4b sets no cookies. No login. No account. Nothing to consent to.

Contact

Operator: Burcevski ICT (KvK 74404172), Amersfoort, the Netherlands.
Contact: open a GitHub issue