Playlist Sorter runs in the Chrome browser, and communicates with the YouTube API, on behalf of the user, to sort videos within a playlist.
In order to do this, Playlist Sorter must ask for the user's YouTube login credentials and transmit them to YouTube. This is done via the standard Google-provided YouTube OAuth user interface, and is encrypted by HTTPS.
Playlist Sorter never stores or transmits the credentials anywhere else. Playlist Sorter has no server of its own.
Playlist Sorter does not store or transmit any user data outside the use of the YouTube API.