SEO: Use canonical tags to reduce duplicate content

Canonical tags are an important tool for preventing duplicate content in organic search results. "Canonical" in search engine parlance means the true side of potentially many duplicates.

Canonical tags are single lines of code in HTML part of a web page. They are invisible to visitors but not to search engines.

Note the example below from Kohl & # 39; s, which assigns a canonical tag for a bedding and sale page.

Kohl's uses a canonical tag on its Bedding and Sales page to reduce duplicate content.

Kohls uses a canonical tag on a bedding and sales page to reduce duplicate content.

How does Canonicals work?

When they come across a canonical tag on a page, the search engine's URL in the tag compares to the URL of the page they are crawling. If the URLs match, the page they are on is the canonical version. If not, bots will consider not indexing that page and assign its link permissions to the canonical version.

In the image above, for example, the URL in the browser field for Kohl's Bedding and Sales page But the canonical tag identifies a nicer version:

Thus, search engines will probably index only the version without the parameter ("? Cc = bed_bath-TN1.0-S-bedbath ”).

How to implement

Most e-commerce platforms include self-referencing canonical tags by default. One page at would have a canonical tag that contains its own URL:

But there are many ways that an e-commerce site creates duplicate content. For, duplicate pages may contain:

  • Tracking parameters:,
  • Different click paths to products that produce different URLs:,
  • A duplicate subdomain:
  • Unfriendly system-generated URLs:

We can ask search engines to ignore the four duplicate pages by inserting the same canonical tag on each page, which, again, is:

Your e-commerce platform can enable you to change canonical tags for each page as easily as changing a title tag. However, the best option is to use canonical tags programmatically, which probably involves a developer.

Canonical tags can also handle syndicated content that appears on multiple websites. The words determine duplicate content, not the design or the font. Similarly, excerpts are published on a site that links to a full version on another duplicate content.

In the absence of a canonical tag, search engines will choose which page to rank based on which was first posted, which has more links, or some other algorithmic method. To assign rank properly, you use canonical tags and force syndication partners to use them as well.

Other options

There are three additional ways beyond tags to specify canonical URLs in the XML Sitemap, in HTTP headers, and with a 301 redirect.

XML Sitemaps show the URLs on your site that you want crawlers to crawl. Done right, XML Sitemaps are effective in delivering canonical URLs. Unfortunately, many websites fail to run Sitemaps correctly or do not list non-canonical URLs, which allows search engines to merge duplicate pages on their own.

PDF files and other file formats that do not contain HTML source code can indicate a canonical URL in the HTTP header. For example, say you have the same text on a web page and a PDF file. You want the web page to be ranked because it contains the site's navigation and calls to action. To do this, place a self-referencing canonical tag on the page, for example:

Then use the page's URL in the HTTP header to prevent PDF from being ranked link tag when the server delivers the PDF:

link: ; rel="canonical"

The syntax is different – even if the elements are similar – because one is a meta tag in HTML code and the other is a statement in an HTTP header.

Remember that canonical tags are only recommendations. Search engines determine which page will be the canonical version, again, based on relevance and authority signals. You can view the canonical page for all URLs that you have verified for access Google Search Console using the URL Inspection Tool.

A more powerful solution for removing duplicate content is a 301 redirect. This powerful canonization tool prompts search engines to (i) index the URL, (ii) request indexing for the new URL (iii) and link the old page's link privileges to the new one. Unlike a canonical tag, a 301 is a command rather than a suggestion.

For more, see "SEO: 7 Ways to Kill Duplicate Content", my post from last year.

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