Canonical Tag

A canonical tag (rel=canonical) is an HTML element that tells search engines which URL is the preferred or master version of a page when similar or duplicate content exists on multiple URLs.

Beginner5 min readUpdated 2026-07-26Reviewed by Lucía Marín

Key takeaways

Canonical tags prevent duplicate content issues by signaling the preferred URL.
Always use absolute URLs and only one canonical tag per page.
Self-referential canonicals are acceptable and common.
Canonical tags are hints, not directives—search engines may ignore them if incorrect.
Combine with sitemaps and 301 redirects for a complete canonicalization strategy.

Canonical tags are a core technical SEO control for managing duplicate content across your site.

Example

Your e-commerce site has a product page accessible via:

https://example.com/shoes
https://example.com/shoes?color=red
https://example.com/shoes?size=10

By adding <link rel="canonical" href="https://example.com/shoes"> to all three URLs, you tell search engines that https://example.com/shoes is the preferred version.

When should I use this?

Use canonical tags when:

You have duplicate or very similar content on multiple URLs (e.g., printer-friendly versions, session IDs, tracking parameters)
You syndicate content to other sites
You use faceted navigation (filtering, sorting) that creates many URL variations
You want to consolidate link signals to a single preferred URL

What it is not

Not a redirect: Users still see the original URL; only search engines see the hint.
Not a guarantee: Search engines may ignore the canonical if it's incorrect or conflicting.
Not a replacement for 301: For permanent moves, use a 301 redirect.
Not a noindex: Canonical does not remove a page from search results; it only suggests preference.

Quick start

Identify the preferred URL for each set of duplicate pages.
Add <link rel="canonical" href="https://example.com/preferred-url"> inside the <head> of all duplicate pages.
Use absolute URLs (including https:// and full path).
Ensure only one canonical tag per page.
Test with Google Search Console's URL Inspection tool.

Common mistakes

Using relative URLs instead of absolute canonical URLs.
Declaring more than one canonical tag on a page.
Pointing the canonical to the wrong protocol, host, or path (e.g., HTTP instead of HTTPS).
Using one canonical across different language versions instead of canonicalizing within the same language set.

Next step

What Is a SitemapLearn how sitemaps complement canonical tags for better indexing.

FAQ

What is a canonical tag?

A canonical tag (rel=canonical) is an HTML element that tells search engines which URL is the preferred version of a page when duplicate or similar content exists on multiple URLs.

How do I add a canonical tag in HTML?

Add <link rel="canonical" href="https://example.com/page"> inside the <head> section of your HTML.

What is the difference between a canonical tag and a 301 redirect?

A 301 redirect sends users and search engines to a different URL permanently, while a canonical tag only signals preference without redirecting. Use 301 for permanent moves, canonical for content accessible via multiple URLs.

Sources

Google Search Central — Most authoritative source for how Google handles duplicate URLs and canonicalization.
Moz Canonicalization Guide — Clear practitioner-friendly overview of canonical tags and duplicate-content handling.
Ahrefs Canonical Tags Guide — Practical SEO explanation of implementation pitfalls and common use cases.
Yoast SEO documentation — Relevant for WordPress implementation context.

Reviewed by Lucía Marín, Founding editor.