Technical SEOPublished26.05.2026

Site mirror (duplicate domain)

A site mirror is an exact or near-exact copy of a website on a different domain or subdomain. It creates a duplicate content problem and dilutes link equity, negatively affecting SEO.

In brief

A site mirror is a technical scenario where the same content is accessible at multiple URLs or domains. In SEO context: multiple domain variants (www/non-www, http/https) or a site copy on another domain without proper redirects or canonical tags.

What is a site mirror

A site mirror is a situation where identical or near-identical content is accessible at multiple addresses. Search robots treat each URL as a separate page and encounter duplicate content, leading to indexing problems and link equity dilution.

The most common case is a site being accessible both with and without www, or via both http and https, without a redirect. Google may choose the 'wrong' version as canonical, causing the main domain to lose its SEO advantages.

Intentionally creating site mirrors (copies on other domains) to rank multiple sites simultaneously violates Yandex and Google guidelines. Yandex has a specific 'primary mirror' mechanism for the legitimate consolidation of domains.

Types of site mirrors

www and non-www
Site accessible via both example.com and www.example.com without a redirect — classic technical mirror.
HTTP and HTTPS
Both http://example.com and https://example.com serve content — a problem from incorrect HTTPS migration.
Trailing slash
example.com/page and example.com/page/ — different URLs with identical content.
Mirror on another domain
Site copy at example.net when the primary domain is example.com. Intentional or leftover from a redesign.
Mirror on a subdomain
mirror.example.com or old.example.com — outdated versions not properly closed.

SEO impact of site mirrors

  • Duplicate content: the search engine may not know which version to index and show
  • Link equity dilution: links pointing to different URL versions don't consolidate — PageRank is split across multiple versions
  • Crawl budget waste: the bot crawls duplicate pages instead of new ones
  • Query cannibalization: multiple page versions compete for the same positions
  • Yandex penalties: Yandex explicitly combats mirror sites and may demote or exclude them

How to fix a site mirror

  1. Determine the canonical URL version: with www or without, with https
  2. Configure 301 redirects from all variants to the canonical version (www → non-www or vice versa, http → https)
  3. Add canonical tags to all pages pointing to the canonical URL
  4. In Google Search Console, specify the preferred domain in settings (change of address)
  5. If there's a mirror on another domain — close it with a 301 redirect to the main domain
  6. Verify sitemap.xml — it should contain only canonical URLs

Primary mirror in Yandex

Yandex has a specific mechanism — the primary mirror. This is the official procedure for consolidating multiple domains or site versions into one primary domain in Yandex's view. Used when: migrating to a new domain, consolidating www and non-www, or changing protocols.

  • Configure 301 redirects from all non-primary domains to the main one
  • In Yandex Webmaster, add all versions and use the 'Site migration' tool
  • Yandex consolidates link equity and passes it to the primary mirror — analogous to 301 redirects in Google
FAQ

Common questions

Check accessibility: http://example.com, https://example.com, http://www.example.com, https://www.example.com — all four should redirect to one. Use Screaming Frog or online redirect checking tools.
Neither is inherently better for rankings. What matters is consistency: pick one and configure redirects from all other variants. Technically, www offers more flexibility for DNS and CDN configuration.
Yes. A 301 redirect from the mirror domain to the primary one transfers link equity (PageRank). Google processes 301 redirects with virtually no loss. The link profiles consolidate on the primary domain.
No — this violates search engine guidelines. For geo-targeting, use: ccTLDs (example.ru, example.de), subdomains (ru.example.com), or subdirectories (example.com/ru/) with proper hreflang setup.
Direct contacts

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