Written by Anthony Godley
CEO, Optima

This is the definitive, accurate and comprehensive guide to using canonical tags. Through this guide, supported by a number of practical examples, you will learn what canonical tags are, how to use a canonical tag properly and how to implement them. You will also learn about common mistakes you will need to avoid.

Lets jump straight in…

In its most simplest form, a canonical tag is a signal within a web page which says, “this piece of content is a copy of another piece of content which you can find at location X”.

This tag tells Google where the other piece of content is, and tells the search engines that the original location of the preferred piece of content. This overcomes the duplicate content issue with Google and other search engines meaning you can add third party content to your website without the risk of duplication penalties; there are things to consider of course which we will get too.

In most cases, when a search engine crawls two or more web pages that has very similar content, they will select only one of the pages to index. That page generally being the one that originally posted the content, although there are a number of factors that are considered. In most cases all other pages with similar content are ignored. You will be able to find them indexed on the search engines but they will have little to no positive effects on the overall website authority, ranking or scoring factors.

Search engines will also look at a range of other factors when deciding which page to index including which page was first crawled, how many backlinks each page has or which one is offering the most internal links.

Duplicate content is extremely bad for SEO, so if you are developing a Search Engine Optimisation strategy, make sure content being produced (web page, blog etc), is fresh and avoid any duplications. Duplicate content can also harm the potential for increased conversion rates as content will not be shown in its best possible form.

As websites grow, it is common that multiple web pages will contain very similar information or content which are vital to the infrastructure of the website environment. This is particularly common with larger sitemaps and eCommerce websites.

If a website has multiple pages with similar content you can add the rel=canonical tag on the preferred source page which will remove the risk of a duplicate content penalty.

What you can see here is 3 of the exact same product being used, with different URLs, which you can see through the breadcrumbs being pointed at by the arrows.This means that the product is shown 3 times, has the same content with only very small variations between them. These products are likely to be hit with a duplication penalty.
What you can now see is the implementation of the Canonical Tag. We have signalled to the search engines that original product is Bats > MRF > Classic which would be the URL (www.optimatech.com.au/bats/mrf/classic). The other two URLs/products are copies of the first product and therefore, because we are telling the search engines that two products are copying the main product through the canonical tag, we avoid a duplication penalty.

There will also be occasions where web page URLs have special characters added at the end of them. These special characters are called parameters and will always follow a question mark in the URL.

For example:

When adding a parameter into the URL, completely different page content is shown despite the URL seemingly pointing at the same page.

There are three different variables setting a parameter in a URL will provide:

  1. The URL parameter will show completely different content
  2. The URL parameter will filter out certain parts of a piece of content
  3. The URL parameter will have no effect

The first thing you need to do is decide which page is going to be set as the preferred URL. Essentially this will be the version of the page you deem to be the most important. You can look at the page with the most links feeding to it, or the page that gets the most visitors.

If you are using a CMS (Content Management System), such as WordPress or Magento, there are a lot of different Canonical Plugins that can be used to apply a canonical link. However, if you are going straight into the code you will need to add a <link> to the <head> section of the additional pages but NOT the preferred page.

The link would look like the below example:

<link rel=”canonical” href=”https://www.optimatech.com.au/bats” />

What this does is demonstrate to the search engines that the preferred URL for visitors wanting to access the bats page. This also tells the search engine that this is the page you would prefer the visitor to reach over the other similar pages.

Yoast is a powerful SEO extension which supports WordPress sites. They have created a very useful GUIDE which helps further explain canonical considerations.

If canonical tags are wrongly used, there can be dire consequences. For example, let’s say you set up your site where your homepage was the preferred web page and each page within the site was a copy of the home page. In this instance, search engines would complete de-index (remove), all your web pages from search results.

There are some common mistakes which need to be avoided:

  • If you have a non dynamic canonical tag on each page of your website which then points to one preffered URL/web page, you will be committing SEO suicide.
  • Multiple canonical tags in a single web page is quite common. Remember search engines will only count the first one meaning anything related to others will be discounted.
  • Always use complete URLs which includes the HTTPS:// section. A common mistake it forgetting this segment of the URL.
  • Do not point product pages to category pages. Product pages always need to be indexed separately.
  • If using a canonical tag on a paginated page you may run into problems.

Paginated URLs are simply a series of URLs which follow each other in sequence. A typical example of paginated URLs would be URLs in a story or a series of products, lists of blog posts etc.

If you were writing a story which had a number of chapters and each chapter was a web page you would likely only want to send users to the first page from the search engine results pages. Then the user could access the second web page from the first web page, the third web page from the second and so on.

In this case a canonical tag would be damaging as pointing every web page/chapter to the first page would mean all content from page 2 onwards would be lost and have no search rank authority at all. This is something you should avoid as users may wish to jump straight to page 2, 3 or 4.

In this instance your paginated pages would be treated as normal web pages. And, search engines would treat them as individual web pages rather than consolidating into one piece of content.

This is a very useful GUIDE which delivers a Pagination SEO Best Practice solution

This is a fiercely debated topic when it comes to best practice SEO.

John Mueller from Google has created a Best Practice GUIDE which is quite useful.

You can avoid the potential risk of a duplicate content penalty by implementing a self referencing canonical and many popular CMS systems will allow these parameters without changing content, such as:

  • https://optimatech.com.au/widgets/widget-1/
  • https://optimatech.com.au/widgets/widget-1/?isnt=it-great
  • https://optimatech.com.au/widgets/widget-1/?cmpgn=twitter
  • https://optimatech.com.au/widgets/widget-1/?cmpgn=facebook

You can use canonical URLs which point to another domain so if you have a piece of content which was submitted to your website but an external site also feels the content would be of benefit to their users, you can use the rel=canonical tag to ensure the URL is linked back to the original content on your site.



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