Helping search engines crawl your website and prioritize the web pages you want users to find is a key objective of SEO. Using canonical tags can improve your ranking on Google and other search engines.

An effective search engine optimization (SEO) strategy is important for every brand with a web presence – particularly e-commerce sites. It is the best way to build awareness about your site and make sure it’s visible to the widest possible audience by improving your ranking on organic search engine results pages (SERPs).

A key aspect of a strong SEO strategy is to make it easy for Google – where 90 per cent of all global searches happen – and other search engines to understand and index your content. This will help drive traffic to the web pages you want to showcase and, ultimately, help you increase sales.

This is easier said than done for one key reason: It’s common for a site to have multiple unique URLs that lead to the same content. For example, a brand may have created different versions of a web page to reflect factors such as regional, device or protocol variations. This is all acceptable and does not violate any of Google’s spam policies. However, as Google points out, “having the same content accessible through many different URLs can be a bad user experience and it may make it harder for you to track how your content performs in search results.”

That’s where canonicalization comes in. Google defines this process as choosing one digital address or canonical URL to serve as the best representation of a web page that has been duplicated. Also called deduplication, it is what allows Google to show only one version of the web page in its search results.

Without guidance from the site owner, Google will determine which of the duplicated pages is the canonical URL that will get highlighted on its SERPs. For search, it simply does not make sense to showcase all the different versions. How does Google choose the canonical URL? It follows two general guidelines: the site’s preference (which URL does it look like the site wants Google to use?) and the user experience (which URL is most helpful for the user?). When it comes to the site’s preference, Google looks to a number of things, including canonical tags, as well as redirects, internal linking, the URL provided in the sitemap file and the encryption protocol used (tip: Google prioritizes HTTPS URLs over HTTP URLs).

If you are a site owner and have a strong preference for the URLs you want shown to seachers, be sure to use those preferences consistently across your website and let search engines know by employing canonical tags to the original URLs.

Here Postmedia unpacks the ins and outs of canonical URLs and canonical tags, what you need to know and best practices.

Canonical URLs and canonical tags explained

A canonical URL is the primary version of a web page that has multiple versions. A canonical tag (a.k.a. “rel canonical”) is an HTML element site owners can use to let Google and other search engines know the preferred, principal or primary version of a web page with alternate versions.

Canonical tags use simple syntax and are placed in the head section of a web page’s HTML source code. Here’s what they look like:

<link rel=“canonical”

href=“” means the canonical version of this page can be found at this URL.

Why canonical tags are important for SEO

Google will only index one version of a web page and it only ranks the web pages it indexes. Using canonical tags puts you, the site owner, in control of the version of a duplicated web page that will be shown to users in search. It will also help you avoid harming rankings by having multiple pages compete for the same spot and help prevent Google from wasting time crawling multiple versions of the same content instead of finding other content on your site worth ranking.

How Google determines the canonical web page

Google’s algorithm considers a range of signals when determining which of multiple duplicate web pages is the primary version. These include but are not limited to:

  • duplicates
  • canonical link elements
  • sitemap URLs
  • internal links
  • external links
  • redirects
  • hreflang
  • PageRank
  • HTTPS pages over HTTP
  • shorter URLs over longer URLs
  • pages over PDFs
  • where content was first published/seen
  • site level signals like a history of scraped content

How to specify a canonical URL

Google spells out five methods to tell the search engine which of multiple duplicate web pages is your preferred primary version:

  • HTML tag (rel=“canonical” link element): Google identifies this as a strong signal. To use this method, add <link> element in the code for all duplicate pages, pointing to the canonical page.
  • HTTP header (rel=“canonical” HTTP header): Send a rel=”canonical” header in your page response.
  • Sitemap: Specify your canonical pages in a sitemap.
  • Redirects: Google considers this a strong signal that the target of the redirect should become canonical and recommends using this method when “you want to get rid of existing duplicate pages. All redirection methods — 301 and 302 redirects, meta-refresh, JavaScript redirects — have the same effect on Google Search, however the time it takes for search engines to notice the different redirect methods may differ.”
  • AMP variant: If one of your duplicate versions is an AMP page, follow the AMP guidelines to specify the canonical page and AMP variant.

If you are using a content management system, you don’t have to worry about re-coding your pages. In many cases, self-referencing canonical tags are automatically added and customization is also possible.

Best practices to implement canonical tags

  • Determine which URLs you want to show up in search results. Include only these canonical URLs in your site map instead of all URLs that lead to the same content.
  • Use absolute URLs in the canonical tag. An absolute URL is the entire web address: the protocol (HTTPS), domain name and the location inside your website where the page you want indexed resides. It will look like something like this:

<link rel=“canonical” href=“” />

  • Use lowercase when creating your URLs.
  • If you have versions of the same page with different protocols, be sure to use the more secure version. For this reason, Google prefers HTTPS over HTTP.
  • Use a self-referencing canonical tag on each canonical page — not just alternate pages. While not required, Google does appreciate them as they make it easier to pick the exact URL you prefer and avoid choosing URLs that have been tagged for other parameters, such as analytics.
  • Only use one canonical tag per page – if you use more than one, Google will likely ignore all of them.
  • When linking within your website, make sure to link consistently to the canonical URL rather than a duplicate URL. This will help Google understand your preferences.

The overarching objective of SEO is to help potential customers find your website. To make that happen, search engines have to discover you first. Canonical tags can help search engines crawl your website and prioritize the web pages you want users to find, improving your ranking in the process.