New format
Site mirror: what it is, why to merge, how to check
A “mirror” in web practice is nearly the same site — or the same content — under another URL: www and non-www, a spare domain, a copy on another host. For search that is a duplicate risk if the addresses are not merged.
Below: three meanings of the term, legitimate reasons for mirrors, how to glue the main host with 301, and how to check. Example `.htaccess` rules live in a separate post; this one covers logic and order.
Three meanings of “mirror”
**Variants of one site:** `example.ru` and `www.example.ru`, http and https — classic host mirrors. Without a merge the engine sees different URLs.
**Synonym domain:** a second address you bought (typo, old name) with 301 to the main one. **Physical copy:** same content on another server for availability or load — SEO still needs one canonical entry for users and the index.
What to remember:
- a mirror is not “another site ranking separately”
- one content set — one main URL in the index
- other hosts return 301 to the canon
Why mirrors are made
Merging www/non-www and http/https is required hygiene. Extra domains protect against typos and similar-name capture. Geo or backup copies are for availability on outages — engineering, not “two sites in the results.”
Do not confuse this with a satellite network: useful content and links to the main domain are not clones built for manipulation.
Legitimate cases:
- one main mirror
- domain move with 301
- typo domains → canon
- country domains with a clear canon / localization
How to merge the main mirror
Pick the canon: usually `https://` plus a www-or-not decision. All other host/protocol variants get a permanent 301 to the canon — including paths, and where possible without long chains.
On Apache people often edit `.htaccess`; on nginx — `return 301` in the config. After the merge check Webmaster / Search Console and the sitemap for canonical URLs.
Order:
- choose the canon
- set 301 from all mirrors
- update internal links to the canon
- serve a sitemap with the canon
- check webmaster panels
Moving to a new domain
The new address becomes the canon: the old domain fully 301s to matching new URLs — page by page, not everything to the homepage. In panels you file a move / address change.
Gradually switch links in email, ads, and partnerships to the new host; keep the old one with redirects while external traffic still arrives.
How to check
Request a non-canonical URL: headers should show `301` and `Location` to the canon. In the browser account for redirect cache — check with a clean request.
In results and index reports see which host is shown. “Merge check” tools are a quick glance; truth remains response headers and webmaster dashboards.
Check checklist:
- http → https
- www ↔ non-www
- synonym domains → canon
- no chains of three or more redirects
- sitemap and internal links on the canon
FAQ
Are www and non-www mirrors?
Yes. For the crawler they are different hosts with the same content until there is a 301 to one canon.
Is Host in robots.txt enough?
For Yandex, Host is outdated. The main fix is a 301 to the canon plus settings in Webmaster / Search Console.
Redirect or canonical?
For host mirrors (www / https / another synonym domain) — almost always 301. Canonical — for parameters and template duplicates on one host.
Do I need mirrors “to escape a filter”?
Moving to a new domain to dodge sanctions is a bad strategy. Fix the cause first; otherwise the filter follows the new name.
How many mirrors are OK?
Technically many synonyms (typo domains), but all should 301 to one main URL. Do not keep several 200 OK responses with the same content.
How do I verify the merge?
Open the non-canon with `curl -I` or DevTools: you should see 301 to the canon. In results and Webmaster — one main host.
Are CDN and geo copies the same?
Similar for availability, but SEO needs one public canonical URL. A CDN usually does not spawn separate index hosts.
How does this relate to HTTPS?
http→https merge is part of choosing the main mirror. See the HTTPS and redirects posts.
www and non-www both answer 200 — and the index quietly doubles?
We’ll pick one https canon, 301 the rest, and verify headers — prep hygiene, not a next-day TOP promise.
Discuss the task
