Canonicalization

Canonicalization is a method used to help prevent duplicate content issues and manage the indexing of URLs in search engines. Using canonicals appropriately can be hugely helpful for SEO.

Implementing the canonical tag link attribute “rel=canonical” is a signal to search engines about the preferred page for indexing, and will be followed in most cases when it is correctly implemented to an equivalent page.

The collected SEO Office Hours notes below provide detailed information and best practices (straight from Google’s own search experts) for using canonicals on your website.

Passing Signals Within a Large Group of Canonicalized Pages Takes Time

November 27, 2018 Source

If a large group of pages is included within a canonicalized set, Google will still have to crawl and process all of these pages to find the canonical and pass on any link equity if the canonicalised pages are linked to externally.


Canonicalizing Paginated Pages Back to Main Page Can Cause Crawling & Indexing Issues

November 13, 2018 Source

Canonicalizing pages in a paginated set back to the first page can be problematic because Google may see that these are different pages and ignore the rel canonical. Alternatively, if Google does follow the rel canonical to the main page, this could mean links and content on other pages might be missed.


Hreflang is a Minor Canonicalization Signal

October 5, 2018 Source

Google uses hreflang as a small signal when picking the canonical version of a page, but this needs to be backed up by consistent signals provided by rel canonicals, internal linking and sitemap files.


Implement Clear Canonical Version Per Country & Hreflang Between Equivalent Canonical Versions

September 18, 2018 Source

Don’t specify a canonical between different country versions of a page, because Google will likely only index the preferred version. John recommends having a clear canonical version per country and implementing hreflang between the canonical versions for each country.


JavaScript Injected Tags Should Not be Duplicated in Static HTML

August 24, 2018 Source

Using JavaScript to modify canonical or robots meta tags can change the signal provided to Google when they come to process the rendered version of the page. If tags are injected using JavaScript, then John recommends not having them in the static HTML so that the signal provided to Google is clear.


Google Doesn’t Support Canonical Tags for Images

June 26, 2018 Source

Canonical tags don’t work for images, so you can’t fold together different sizes of an image to make sure only the best size is indexed, for example. Google is looking into how best to use srcset for image search, however.


Canonical Selection Doesn’t Affect Rankings For a Group of Pages

June 26, 2018 Source

Google will simply show one URL out of a group of pages that have been canonicalised. The ranking will be the same for that group of URLs no matter which one Google decides to show.


Different Signals Determine Google’s Canonical Selection

June 26, 2018 Source

John confirmed that rel canonical, redirects, internal linking, URL parameters and sitemaps are all signals Google uses to decide which page is the canonical from a group of pages that have been folded together.


Canonicalise Duplicate Pages Between Your Sites so They’re Not Seen as Doorway Pages

May 29, 2018 Source

Use the canonical tag if you are offering the same products on lots of different sites so Google doesn’t suspect that these are doorway pages.


Related Topics

Crawling Indexing Crawl Budget Crawl Errors Crawl Rate Disallow Directives in Robots.txt Sitemaps Last Modified Nofollow Noindex RSS Fetch and Render