Canonicalization is a method used to help prevent duplicate content issues and manage the indexing of URLs in search engines. Implementing the canonical tag link attribute “rel=canonical” is a signal to search engines about the preferred page for indexing, and will be abided to in most cases when it is correctly implemented to an equivalent page. Our Hangout Notes on canonicalization provide best practice advice and insights for how it is handled by search engines.

Use Canonical Tags to Resolve Trailing Slashes

June 28, 2016 Source

Canonical tags are the best way to deal with trailng slash duplicate pages.

Don’t Use Noindex on Canonicalised Pages

May 17, 2016 Source

Don’t mix Noindex with canonical to a different page.

Many to One Canonical Tags May Be Ignored

May 17, 2016 Source

Google will try to follow canonicals by default, but they ignore canonical tags if there are significant content differences, or if a lot of URLs canonicalising to the same page, if they think it’s a mistake.

May 6, 2016 Source

Publishing multiple versions of a page on different sites, and canonicalising to a single page for link building, is not acceptable. The duplicates should be nofollowed.

Google May Choose an HTTP URL as Canonical if the HTTPS has Mixed Content

January 29, 2016 Source

Google will try and choose a canonical URL which does not have mixed content issues from http/https. I.e. if there is an https version of a page that DOES have mixed content issues, but an http version that does NOT have mixed content issues, then the http version could be used. If however, there are very strong signs to use that https version coming from the website, (such as redirects or rel=canonicals) then Google will still use the https version even though it has mixed content issues.

Don’t Mix Noindex and Canonical

December 1, 2015 Source

Having a page with a canonical tag pointing to a page with a noindex is a problem but the canonical might just be ignored.

Canonicalising Product Variants Loses Unique Content

December 1, 2015 Source

If you have product variant pages, instead of noindexing, you are better to canonicalise the variations to a single version which can consolidate all the ranking signals. However you will lose any unique content from those variations.

Googlebot Can Be Redirected to Canonical URLs

December 1, 2015 Source

John says that althought it’s technically cloaking, it’s actually OK to redirect Googlebot from URLs with tracking parameters to canonical URLs, but allow users not to be redirected, so they can be tracked in analytics.

Duplicate Pages with a Noindex May Be Selected

October 27, 2015 Source

If you have duplicate pages with the same content which aren’t canonicalised, but one of the pages has a noindex, then Google might pick the noindex version, and then that page will be noindexed even if there is an indexable duplicate.

Related Topics

Crawling Indexing Crawl Budget Crawl Errors Crawl Rate Disallow Sitemaps Last Modified Nofollow Noindex RSS Fetch and Render