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What is Canonical tag
This means that Google considers the canonical tag as a strong hint, but ultimately, it takes many signals into consideration and decides whether to respect them or not.The canonical tag is not a directive like a Robots.txt file.
The canonical tag came into its own in 2009 as an HTML tag in the source code that tells search engines which URL is the master version of a page. This can be used to tell Google which page variations it should index for users.
There are two simple ways to define canonical variants: user-declared canonical and Google-declared canonical.
User-declared specification: This is exactly what it says; it is the specification specified in the specification tag.
Google’s declared canonical: This is the URL that Google has chosen as canonical.
How Google chooses canonical URLs
When Google crawls and indexes a website, it looks at the main content on the page.During this crawl, it may discover similar pages, and Google will then select the page that it thinks best represents what the page is trying to convey to the user and choose it as the canonical page.Internal and external links are just a few additional factors that Google considers with canonical tags.
Note: If you link your pages internally using query parameters like /?some_parameter=xyz , there’s a good chance Google will ignore your canonical meta tag and choose the URL with the query parameter as canonical.
Google crawls RSS very aggressively, so make sure the canonical you declare matches the URL in your RSS feed.
If you add URLs to your RSS feeds with parameters like /?source=feed to track website traffic from RSS subscribers, there is a chance that Google will pick up the canonical with the query string /?source=feed, even though this is a tracking parameter — and Google knows that.
You can use a link shortening service for the URLs in your RSS feeds to be able to track clicks on them or use an RSS service like FeedPress.
Google also makes choices for the sake of user experience.
If you have a desktop version of your site, Google may serve the mobile version to users on mobile devices.
How Canonical Tags useful with SEO
Canonical tags are crucial for sites with a handful of pages as well as sites with millions of pages.
You select the canonical tag
The canonical tag gives you the opportunity to suggest to Google the best version of a page on your site that you would like to serve to users.
Repeated content
Duplicate content is one of those areas that seems simple on the surface but is more complex than its name would suggest and often carries negative connotations.
So you might be thinking, “I don’t have any duplicate pages,” but before you make that statement, let’s take a quick look at what can be defined as “duplicate” via the Google Search Center documentation.
Duplicate pages can be categorized as any page that contains the same primary content in the same language. Let’s say you use different pages to support mobile pages (m., amp, etc.) and dynamic URLs that facilitate things like parameters or session IDs.
In this case, your blog creates paths in multiple folders; you have HTTP and HTTPS versions of your site, and your site has duplicate content. This is nothing to panic about and is very common, hence the importance of canonicalization!
Google uses Canonicals as its primary source
Google uses canonicals to determine the content and quality of a page.
Canonical pages are crawled more frequently than non-canonical pages.
May help with crawl budget
If you have a relatively large website, you may have heard the term “crawl budget”.
If done correctly, canonicals can help reduce the burden on your crawl budget because Google will crawl the canonical version of a page more often than the non-canonical version.
This is not a replacement for no-index tags, redirects, or robots directives。
Integrate link signals
Canonicals direct search engines to take the various information they provide for multiple similar pages and combine it into a single URL, increasing its value.
Content Syndication
If you have a site that has its content syndicated or leveraged by partners, you want to make sure it’s your version that appears in search results.