(I'm the author), I don't blame you for being concerned, but I can assure you that no personal data leaves your computer. The processing happens by accessing G

(I'm the author), I don't blame you for being concerned, but I can assure you that no personal data leaves your computer. The processing happens by accessing Gmail metadata and processing on the client-side. Feel free to inspect the source (which is in JS, although it has been minified) or watch outgoing requests.