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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.

For more on canonical tags and related topics, check out Lumar’s additional resources:

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

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.

18 Sep 2018

JavaScript Injected Tags Should Not be Duplicated in Static HTML

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.

24 Aug 2018

Google Doesn’t Support Canonical Tags for Images

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.

26 Jun 2018

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

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.

26 Jun 2018

Different Signals Determine Google’s Canonical Selection

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.

26 Jun 2018

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

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.

29 May 2018

Make Sure A Separate PWA is Canonicalised to Your Mobile Site

Google won’t get confused between your main site and separate PWA as long as you have canonicalization in place.

29 May 2018

Internal Linking Causes Google to Crawl Canonicalised Pages

Check your internal linking if you see Google crawling canonicalised pages.

29 May 2018

Hreflang Should be Included Between the Canonical Versions of Pages

Including hreflang on paginated pages is fine but the most important thing is to include hreflang tags between the canonical versions of the page.

18 May 2018

Parameter Handling Signals Are Stronger Than the Canonical Signal

Google won’t blindly follow URL parameter handling set in GSC, but John says that this is a stronger signal than using canonicals.

15 May 2018

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