A Canonical Tag (rel=”canonical”) is a snippet of HTML code that tells search engines: “This is the master version of the page. Ignore all other duplicates and index this one.”
It is your primary defense against duplicate content issues, ensuring that your “link juice” (ranking power) isn’t split across multiple similar URLs.
1. The Concept: Consolidating Power
Imagine you have three URLs that show the exact same content:
- example.com/shop/blue-shirt
- example.com/shop/blue-shirt?size=small
- example.com/shop/blue-shirt?source=newsletter
Without a canonical tag, Google sees three separate pages. If Page 1 gets a link from a blog and Page 3 gets a link from Facebook, your ranking power is split 50/50.
You place a canonical tag on all three pages pointing to example.com/shop/blue-shirt.
- Google counts all links as belonging to the “Master” URL (Page 1).
2. How to Implement It
The tag goes in the <head> section of your HTML.
The Code:
HTML
<link rel=”canonical” href=”https://example.com/shop/blue-shirt” />
Implementation Methods:
- WordPress (Yoast SEO / RankMath):
- Go to the “Advanced” tab of the SEO plugin on the page editor.
- Look for the “Canonical URL” field.
- Enter the URL of the “Master” page. (If left blank, these plugins usually default to self-referencing, which is good practice).
- Shopify / Wix / Squarespace:
- These platforms typically handle standard canonicals automatically. However, you can often edit them in the page’s “SEO Settings” if you need to point a duplicate page elsewhere.
- These platforms typically handle standard canonicals automatically. However, you can often edit them in the page’s “SEO Settings” if you need to point a duplicate page elsewhere.
3. The “Self-Referencing” Canonical
It is an SEO best practice for every page to have a canonical tag, even if it is the only version.
- Your “About” page is example.com/about.
- It should point to https://example.com/about.
- This prevents scrapers or URL parameters (e.g., example.com/about?fbclid=123) from accidentally creating duplicates in Google’s index.
4. Cross-Domain Canonicals (Syndication)
If you publish an article on your blog, and then repost it on Medium or LinkedIn, you risk outranking yourself.
- Ask the external site to add a canonical tag pointing back to your original article.
- Many platforms (like Medium) allow you to set this in their “Import” or “Settings” menu.
A “Hint”, Not a Directive
It is important to remember that Google treats the canonical tag as a strong suggestion, but not an absolute command.
If you canonicalise Page A to Page B, but Page B is broken (404) or has totally different content, Google will ignore your tag and make its own decision.
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