Data is stored solely in your browser for later use.
It will not be uploaded anywhere, this tool runs entirely in your browser.
Flutter can be installed as a PWA if your browser supports that, or you can just save this page to an HTML file and open it.
* PluralKit's format has become something of a de-facto standard, so other JSONs also work here — such as /plu/ral, and many tools such as Simply Plural can export in PluralKit's format.