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.
For more on canonical tags and related topics, check out Lumar’s additional resources:
Don’t Noindex Canonicalised Pages
You shouldn’t noindex pages which are canonicalised, otherwise they might ignore the canonical tag.
Don’t canonicalise groups of pages to a single URL
Canonicalising a large number of pages to a single page will probably be ignored.
Canonicalised Pages Show up in Google’s Index
Canonicalised pages will still show up for site: searches, but that doesn’t mean the canonical tags aren’t working.
Submit Canonical URLs in Sitemaps and Other References
Use consistent canonical URLs in Sitemaps and other internal references.
Hreflanged Pages in the Same Language Don’t Need to Be Duplicates
If you connect pages together with hreflang which are in the same language e.g. UK/US/Australia, they don’t need to be duplicates. They are allowed quite a lot of variation as if they were different languages.
Use Pagination to Join Split Pages
If you want to split up a page into 2 different URLs, you can’t redirect or canonicalise from the old URL to both new URLs. You can choose one of the new pages as the main one, and link to the secondary page. And you can paginate the pages together.
Canonicalise Product Variants
A discussion around when to canonicalise pages to other pages. e.g for colour variations of product pages.
URL Issues Create Duplicate Pages
Duplicate URLs from inconsistent ordering, case inconstistency, and session IDs can be fixed with canonical tags if the issue is minor, but it still creates crawling issues if there are many instances.
Search Console Reports Canonicalised Pages with Duplicate Titles
Search Console will report pages as having duplicate titles, even if they have been canonicalised
Order of Content for canonicalization Doesn’t Matter
When Google is checking to see if pages are similar for the purpose of verifying canonicalization, the order of the content on the page doesn’t matter. Google can detect when the same content is in a different order on the a page. E.g. a set of identical search results in a different order.