BGG Uploader runs only on your own BoardGameGeek collection page and communicates only with boardgamegeek.com, using the browser session you are already logged in with.

Data sent: the game names you paste are sent to boardgamegeek.com as search queries, and the resulting collection additions or status changes are sent to boardgamegeek.com to update your collection. This is the same data the site's own "Add a Game" form sends.

Data stored: none. The extension keeps your list in memory only while the panel is open and stores nothing on your device or anywhere else.

Data shared with the developer or third parties: none. The extension has no analytics, no telemetry, and contacts no server other than boardgamegeek.com.

Source code: https://github.com/Jecoms/bgg-uploader