Duplicate content: how to find and fix it with canonical

Duplicate content is the same (or very similar) page available at multiple URLs. Search engines may not know which version to show, link equity gets diluted, and indexing suffers. This guide explains how to find duplicates and fix them with canonical tags and redirects.

What counts as duplicate content

Exact duplicates

The same content at different URLs:

• example.com/page and example.com/page/
• example.com/page and example.com/page?utm_source=google
• http://example.com/page and https://example.com/page

Partial duplicates (near-duplicates)

Similar content with minor differences:

• Category pages with minimal unique text
• Product pages with identical descriptions
• Pagination pages (page=2, page=3)

Internal vs. external duplicates

Internal duplicates are on your site. External duplicates are your content copied to other sites. Canonical tags primarily address internal duplicates.

Causes of duplicates

URL parameters

Sorting, filters, UTM tags, and session IDs create variations of the same page:

/catalog
/catalog?sort=price
/catalog?sort=name
/catalog?color=red
/catalog?utm_campaign=summer

Technical variations

• http vs. https
• www vs. non-www
• Trailing slash vs. no trailing slash
• Letter case (for case-sensitive servers)
• Duplicate entries in the sitemap

CMS and site structure

• Print pages (?print=1)
• Mobile versions (m.example.com)
• Pagination
• Date and tag archives
• RSS versions

Content

• Copying and pasting between pages
• Templated product descriptions
• Minimal unique content on category pages

How to find duplicate content

Google Search Console

The “Coverage” or “Pages” report shows indexed URLs. Look for pages with similar titles and descriptions. “Excluded: duplicate without user-selected canonical” is a clear sign.

Search by content

Copy a unique phrase from the page and search for it in Google in quotation marks. If other URLs on your site appear with the same text, they are duplicates.

Site audit

The reChecker technical audit checks canonical tags, redirects, and URL structure. It identifies common sources of duplicates.

Log and sitemap analysis

Check which URLs are included in the sitemap. Make sure each URL is unique or has a canonical tag pointing to the primary version.

Specialized tools

Tools such as Screaming Frog, when available, crawl a site and find pages with identical or similar content based on metrics such as word count and title.

Fixing duplicates with canonical

When to use canonical

• URL parameters (sorting, filters, UTM tags)
• Pagination
• Print versions
• Pages that should remain accessible but should not be indexed separately

Add a canonical tag to each duplicate page pointing to the preferred URL:

<!-- На /catalog?sort=price -->
<link rel="canonical" href="https://example.com/catalog" />

<!-- На /catalog?page=2 -->
<link rel="canonical" href="https://example.com/catalog" />

Self-referencing canonical on the canonical page

The preferred page should point its canonical tag to itself:

<!-- На /catalog -->
<link rel="canonical" href="https://example.com/catalog" />

For more on configuration, see the canonical URL guide.

Fixing duplicates with redirects

When to use a 301 redirect

• http → https
• www → non-www (or vice versa)
• Old URLs after restructuring
• Pages users do not need (duplicates without parameters)

A redirect completely removes the duplicate from access. Users and crawlers land on the target URL.

# Nginx: редирект с www на non-www
if ($host = 'www.example.com') {
    return 301 https://example.com$request_uri;
}

Canonical vs. redirect

Fixing duplicates with content

For near-duplicates (similar content), canonical tags and redirects are not always appropriate. The content needs to be differentiated:

• Write unique product descriptions
• Write unique text for category pages
• Combine thin pages into one page with sections

Checking canonical

The reChecker canonical checker checks markup and identifies errors. Make sure that:

• The canonical points to an existing page
• There are no chains (A→B→C)
• The canonical page returns 200

Duplicate-fix checklist

Index update time

After canonical tags are implemented, Google recrawls the pages. The index may take anywhere from a few days to several weeks to update. Speed up the process by requesting indexing in Search Console for key pages.

Duplicates across domains

Content syndication

If your content is published on partner sites, the canonical on your site points to your version as the original source. Partner sites can canonicalize to your site or use noindex, by agreement.

Mirrors and copies

For mirror sites and copies on other domains, use a canonical pointing to the primary domain. If you do not control the copy, you can request its removal through the DMCA or similar procedures.

Duplicates within one domain: common scenarios

Session IDs in URLs

example.com/page?sessionid=abc123
example.com/page?sessionid=xyz789

The same content has different URLs. Solution: do not add session IDs to URLs for indexable pages, or use a canonical pointing to the version without parameters.

Sorting and filters

/catalog?sort=price
/catalog?sort=name
/catalog?brand=apple

Use a canonical pointing to /catalog. If filtered pages have unique content (for example, “Apple laptops” is a separate page), use a canonical pointing to that page rather than the general catalog.

Regional variations

For multilingual or multiregional sites (one language, different regions), use hreflang, not canonical. Canonical is not used to link regional versions.

Preventing duplicates

During development

Set a single canonical URL from the start. Configure clean URLs without unnecessary parameters. Use 301 for old URLs when changing the site structure.

When adding content

Check that new content does not duplicate existing content. Use unique meta descriptions and titles for each page. Add unique sections to templated content.

Regular audits

Check for duplicates quarterly using Search Console and audit tools. New parameters and sections can unexpectedly create duplicates.

Tools for finding duplicates

Copyscape, Plagiarism

For finding external copies of your content. Enter a URL or text, and the service will find similar pages on the internet. Useful when you suspect content theft.

Siteliner, Screaming Frog

Analyze internal duplicates by similarity. They compare page content and identify near-duplicates, providing a list of pages with a high percentage of matching content.

Google Search

Search for a unique phrase in quotation marks. If several URLs from your site appear, those are internal duplicates. A simple method that requires no additional tools.

Related materials

For the basics of canonical, see the canonical URL guide. To check markup, use the canonical checker tool and the technical audit on reChecker.