Canonical tag
An HTML tag telling search engines which version of a duplicate or near-duplicate page is the master one to index.
In depth
What it really means
When the same content is reachable at several URLs, engines have to pick one to index. The canonical tag is you making that choice explicitly rather than leaving it to them.
It is a hint, not a directive. Google can and does ignore canonicals it disagrees with, usually when the tag contradicts other signals like internal links or sitemaps pointing elsewhere.
How it works
- A rel=canonical link tag in the head names the preferred URL.
- Crawlers treat it as a strong hint about which version to index.
- Signals from duplicate versions consolidate onto the canonical.
- Conflicting signals elsewhere on the site can override it.
Pros & cons
Pros
- Consolidates ranking signals instead of splitting them across duplicates.
- Solves parameter and tracking-URL duplication cleanly.
- Cheap to implement and low risk when done correctly.
Cons
- It is a hint, so it can be ignored.
- A wrong canonical can deindex a page silently.
- Chained and conflicting canonicals are common and hard to spot.
Common mistakes
- Canonicalizing every page to the homepage, which deindexes the site.
- Self-referencing canonicals that point to a non-canonical version, such as http instead of https.
- Canonical pointing one way while internal links and the XML sitemap point another.
- Using canonical to handle pagination, which it was never designed for.
Best practices
- Put a self-referencing canonical on every page as the default.
- Use the absolute URL, with the correct protocol and trailing slash convention.
- Make internal links and the sitemap agree with the canonical.
- Use a 301 redirect rather than a canonical when the duplicate should not exist at all.
FAQs
What is a canonical tag?
An HTML tag naming which version of duplicate or near-duplicate content should be treated as the master for indexing.
Does Google always follow the canonical tag?
No. It is a hint. Google frequently picks a different canonical when internal links, sitemaps or redirects contradict the tag.
Canonical or 301 redirect?
Redirect when the duplicate should not be reachable at all. Canonical when both URLs need to stay live, such as a product reachable through two categories.
Should every page have a canonical tag?
Yes, self-referencing by default. It costs nothing and it removes ambiguity when tracking parameters get appended to your URLs.
Keep reading
Related on LymLyt
Beyond LymLyt
Further reading
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