This app has no server. There is nothing to leak because there is nothing to send.
The files you import are read in the browser and the declaration is generated in it. No request leaves the page: the site's Content Security Policy enforces it (connect-src 'none'), so the browser would block any attempt — including a mistake of mine.
Three keys in the browser's local storage: the declaration in progress (declara720:v2), the language and the theme. That is all — no cookies, no analytics, no identifiers.
The Delete saved data button in the first card, or your browser's site data. Once deleted there is no copy: there is no server holding one.
Open your browser's developer tools, go to the Network tab and reload. After the page loads you will not see a single request.
It is generated on your machine and goes to your downloads folder. It does not pass through anything in between.