Canonical Tags – How it can be used to fix duplicate content

Duplicate Content can bring down the SERP rankings as mentioned in our previous article in which we pressed on Canonical URL Tags as a potential solution to that problem. Today, we will learn Canonical Link Tag, know how to use it effectively and create websites optimized for search engines.

How Canonical tag solves the problem of duplicate content?

Canonical is a value written in ‘rel’ field of the link tag. If search engines come across a webpage with canonical tag in it, they understand that it is the duplicate version. A URL is provided in the link tag which points to original version of the content. Google, Yahoo and Bing have stated that they will treat the canonical tag very closely to permanent 301 redirection which carries forward 90-95% of all the link power to the original page. Read more about Fixing Duplicate Content.

Use the Canonical Tags to redirect to original URL.

After indexing, Google ranks each page with a PageRank. PageRank or commonly called as ‘PR’ is a score on a scale of 10. PageRank is calculated taking in account several factors, of which, duplicate content is one of the factor. Search engine may be right or wrong in selecting the original page in this context. Even though search engines are becoming smarter day by day, we can’t totally leave the entire decision on them. The best possible way to prevent this problem is to restrict search engines from indexing the duplicate pages using robots.txt or show them a path to the original version of content (webpage) using Canonicalization.

How to use canonical?

Suppose your blog is reachable with the URL http://www.examplestore.com/blog/ , as well as with http://www.examplestore.com/index/blog, then you should include canonical tag in a webpage you feel is a duplicate page and point it to original URL.

You can use similar HTML code as shown below in the appropriate webpage so that search engine understands that it is indeed the duplicate URL and redirects to the original URL as mentioned by you.

Canonical tag example.

Canonicalization is an effective in solving the problem of duplicate content which arise due to:

  1. Without proper prefixes and suffixes such as
    • http://
    • www
    • trailing slashes
  2. URLs with embedded Timestamps & Session IDs
  3. These are one of the most common reasons of duplicate content. Session IDs and Timestamps are some sequential numbers mostly used by e-commerce websites which are appended into the URL for either sorting or session management. Alternatively you can use cookies but if it is not possible to use cookies then the problem can be solved with Google Webmasters Tool. There is a section in Google Webmasters Tool where you can enter your pattern to define timestamps or session IDs and they won’t consider that particular section of URL. Learn more about it here.

    Examples

    1. http://www.example.com/
    2. http://example.com/
    3. www.example.com/
    4. example.com/
    5. http://74.125.236.212
    6. http://www.example.com/index.html
    7. http://www.example.com/default.aspx
  4. Capitalization errors also result in multiple URLs.
  5. You can use canonicalization in the situations where the duplicate content problem arises due to capitalization errors in linking URLs as shown in the example.

    Duplicate content error due to alphabetical casing error in URLs

Are there any alternatives to Canonical Tags?

Alternatively, you can use a 302 Temporary Redirect. However, when a search engine comes across it, doesn’t carry forward the page domain and the backlinks of the current webpage to the new URL, which a 301 Permanent Redirect does. The 301 Permanent Redirection is the real solution to solve the problem of duplicate content but it needs either server-side programming knowledge or using server software (Apache or IIS) which everybody may not be comfortable with. So, canonicalization is a very simple and useful in comparison to both of them.

Verifying canonical tag usage in your site?

SearchEnabler SEO Platform showing the webpages using the Canonical Tags to redirect to original URL.

Online SEO platform like SearchEnabler can help you to track duplicate content issues, so that you can use appropriate solutions like canonicalization.
Details like duplicate title, duplicate content are identified as well as canonical URL’s along with page URL’s are highlighted. It helps in correcting erroneous implementation of canonical or identify cases where canonical is missed.

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