How do I check if a site is a mirror of another site?

Add the URL of the site you want to check in Yandex.Webmaster.

If the site is identified as a secondary mirror, it is automatically added to the service together with its main mirror. If the sites are not mirrors, they will be displayed separately.

If your site is combined in a mirror group with someone else's site, it will look like this after you add it to Yandex.Webmaster: