hi renato, everything runs right in your browser, nothing gets sent anywhere. For full offline mode just download the HTML and open it on an air-gapped machine (Tails works great). Once the file’s local, you don’t need the network at all.

Source: https://github.com/bitpanter/bip39-visual — see dist/bip39-visual.html and Releases. Offline: Download the HTML and open it locally (e.g. on Tails). All math runs in the browser.