Watchmarker for Youtube is a free Chrome add-on developed by sniklaus. This add-on addresses the issue of Youtube only marking recently watched videos as watched. With Watchmarker, your entire watch history is tracked and videos are automatically marked as watched.

One of the main features of Watchmarker is its support for the new Youtube theme. Unfortunately, it does not work with the old theme. If you are unsure which theme you are using, it is likely the new one.

To ensure the persistence of your watch history, Watchmarker provides an export and import feature. This allows you to easily create a backup of your history and archive it for safekeeping.

If you want to make sure that your watch history is complete, you can manually initiate a complete synchronization in the settings. This will incorporate as much of your history as possible, beyond the automatic synchronization of recent activity.

In the event that something is not working properly, it is recommended to file an issue on Github rather than leaving a demanding review. Watchmarker is a free extension developed in spare time, and the developer appreciates considerate feedback and bug reports on a platform that is easier to track.