YouTube Secret Dark Mode is a Chrome add-on developed by stemarcoh. This free program enables YouTube's secret dark mode by setting a known cookie to enable server-side styling and a new page layout from YouTube itself. Unlike other extensions, YouTube Secret Dark Mode does not change the HTML or style sheets after they are downloaded.

Upon the first time it is enabled and you load youtube.com, a desktop notification will be displayed, indicating that you will need to reload the page and enable Dark Mode in the settings menu to see it in dark mode. This add-on provides a convenient way for users to enjoy YouTube in a darker theme, reducing eye strain and providing a different visual experience.

Please note that as of 2-May-2017, YouTube has officially introduced dark mode, rendering this extension unnecessary. Users can now enable dark mode directly from YouTube's settings menu.