TMSync by sal

TMSync records your progress to the trackers you connect, and it can update several of them at once. Watch something a single time and every connected tracker stays in sync automatically. Works with Trakt, WeTrakr, AniList, MyAnimeList, and Simkl.

How it works
TMSync reads what is playing (title, season, and episode) from the page and the video player, then records your progress for you. Coverage is defined by lightweight "recipes." Not covered yet? Use the built-in picker to add it in a few clicks.

More than tracking
• Rate what you watch and keep a private note per item, synced back to your tracker (Simkl takes ratings only).
• Handy shortcuts on your tracker pages take you back to where you watch.
• Keeps your lists in sync. List sync reads every connected tracker, shows you the plan (episodes, status, ratings, and anything it would remove), and writes it only when you apply.
• Backs up your sites, quick links, and corrections to a file, and exports your Trakt or WeTrakr movie history to Letterboxd as a CSV.
• Works in Chrome and Firefox.

Privacy by design
There is no backend. Your viewing activity and login tokens stay in your browser and are sent only to the trackers you connect, never to the developer or anyone else. Access is requested only for the pages you explicitly enable, never everything at install.

Open source: https://github.com/kasusoba/TMSync