Playlist Length for YouTube™ runs only on www.youtube.com. When you open a playlist there, it sends that playlist's ID to playlistduration.com, which answers with the videos' durations. Nothing about you and nothing else from the page is sent; the request is logged by the site like any other visit (IP address, browser and country, kept for at most 7 days) and counted, as a total, as coming from the extension. The videos you finish and your playback speed are stored in your browser by the extension and never sent to us; the "Plan schedule" link carries your watched videos after the # in its address, a part browsers do not send to servers. The extension reads nothing on YouTube except the page address and the video player's position and speed, and has no analytics and no ads. Removing it deletes everything it stored. Full policy: https://playlistduration.com/privacy#extension