# Mirror site

Category: [Technical SEO](https://seo-geo-glossary.com/en/glossary/category/technical-seo/) › [URLs & domains](https://seo-geo-glossary.com/en/glossary/category/technical-seo/urls-domains/) · Also known as: mirror, website mirror

A **mirror site** is a replica of a website hosted on a different server under a different URL. In SEO, the concern is identical content being available at more than one address.

## What are mirror sites used for?

The term covers two different situations.

- **Legitimate mirrors.** According to Wikipedia, operators run mirrors to reduce traffic on a main server, speed up access, keep content available and provide backups. They are common for software archives and open-source downloads, for example Linux distributions. Modern mirrors support HTTPS and IPv6.
- **Copied content.** Third parties copy a site onto their own domain. Google's spam policies call taking content from other sites to manipulate rankings scraping and list republishing it with only minor changes as an example.

## Mirror sites and SEO

Several URLs with the same content give search engines a duplicate problem. Google recommends telling it which address is preferred. The documentation names redirects and `rel="canonical"` as strong signals and listing the URL in a sitemap as a weak one. Without a signal, Google picks the version it considers best for users. It advises against using robots.txt for canonicalization, because a blocked URL can still be indexed without its content.

For a mirror you run yourself, each copy can carry a canonical tag to the original or redirect to it with a 301, so that the original is the version shown in results.

## Example

```html
<!-- On the copy https://mirror.example.com/guide/ -->
<link rel="canonical" href="https://www.example.com/guide/">
```

## Common mistakes

- A mirror without a canonical tag or redirect, so two domains compete for the same queries.
- Blocking the mirror in robots.txt as a canonicalization method.
- A forgotten test server or old domain copy that stays indexable.

## Related terms

- [301 redirect](https://seo-geo-glossary.com/en/glossary/301-redirect/index.md)
- [Duplicate content](https://seo-geo-glossary.com/en/glossary/duplicate-content/index.md)
- [Canonical tag](https://seo-geo-glossary.com/en/glossary/canonical-tag/index.md)
- [Scraped content](https://seo-geo-glossary.com/en/glossary/scraped-content/index.md)
- [CDN (content delivery network)](https://seo-geo-glossary.com/en/glossary/cdn/index.md)

## Sources

- [Mirror site – Wikipedia (secondary)](https://en.wikipedia.org/wiki/Mirror_site)
- [How to specify a canonical URL – Google Search Central](https://developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls)
- [Spam policies for Google web search (scraping) – Google Search Central](https://developers.google.com/search/docs/essentials/spam-policies)

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Last updated: October 7, 2026
URL: https://seo-geo-glossary.com/en/glossary/mirror-site/