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Technical SEO

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.

Also called
rel=canonical, canonical link element
Applies to
HTML pages, non-HTML resources via HTTP headers
Commonly confused with
hreflang tags, 301 redirects, noindex

Key points

  • Canonical tags consolidate duplicate URLs into one preferred page for indexing.
  • They help concentrate ranking signals on the version you want to rank.
  • Use absolute URLs in the canonical href, not relative paths.
  • A page should contain only one canonical tag.
  • Self-referential canonicals are acceptable and common.

How it works

A canonical tag is placed in the HTML <head> as <link rel="canonical" href="https://example.com/page">. It signals to search engines that the specified canonical URL is the preferred version among pages with similar or identical content. Search engines treat this as a strong hint but may ignore it if signals conflict, such as when internal links point elsewhere or the content differs significantly. For non-HTML resources like PDFs, the canonical can be sent via an HTTP header. Best practice is to use an absolute URL to avoid ambiguity.

Why it matters

Canonical tags are a core technical SEO control for managing duplicate content. Without them, search engines may split indexing signals across multiple URLs, diluting ranking potential. By consolidating link equity onto one preferred URL, canonical tags help improve the page's visibility. They also make crawling more efficient by reducing the number of duplicate URLs processed. However, they are not a fix for thin content or crawl traps.

What it is not

  • It is not a 301 redirect: a canonical tag does not redirect users or bots; it only suggests the preferred URL for indexing.
  • It is not a replacement for hreflang tags: language variants need hreflang to indicate language and region, while still using canonicals within the same language set.
  • It is not a noindex directive: a canonical tag does not prevent a page from being indexed; it only indicates which URL should be considered the primary one.
  • It is not a guarantee: search engines may ignore the canonical if signals are inconsistent.

Common mistakes

  • Using relative URLs instead of absolute canonical URLs: this can cause confusion if the page is accessed via different protocols or paths.
  • Declaring more than one canonical tag on a page: search engines may ignore both.
  • Pointing the canonical to the wrong protocol, host, or path, e.g., HTTP instead of HTTPS: this undermines the intended preference.
  • Using one canonical across different language versions instead of canonicalising within the same language set: this conflicts with hreflang.
  • Implementing a canonical that contradicts internal links, sitemaps, or redirects: this can cause a canonical error.
Read next Robots.txt Understanding robots.txt helps you control which URLs search engines can crawl, complementing canonical tags to manage duplicate content and crawl efficiency.

Questions people ask

What is canonical tag?

A canonical tag is an HTML element that tells search engines which URL is the master version of a page when duplicate or similar content exists on multiple URLs. It is placed in the <head> section of a page or sent via HTTP headers for non-HTML resources. Search engines use it as a strong signal to consolidate indexing signals onto the preferred URL.

How to add canonical tag in HTML?

To add a canonical tag in HTML, insert <link rel="canonical" href="https://example.com/preferred-page"> inside the <head> section of the page. Use an absolute URL to avoid ambiguity. Ensure there is only one canonical tag per page.

How to use canonical tag in SEO?

Use canonical tags to indicate the preferred URL when you have duplicate content from faceted navigation, tracking parameters, print versions, or syndication. Place the tag on each duplicate page pointing to the master URL. Also use self-referential canonicals on the preferred page itself. Combine with hreflang tags for language variants, not as a replacement.

What is canonical URL in WordPress?

In WordPress, the canonical URL is the preferred URL for a post or page, often set automatically by SEO plugins like Yoast. You can also add it manually via the theme's header.php or using a plugin. WordPress may generate self-referential canonicals by default, but customisation is possible.

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Sources

  1. Google Search Central Most authoritative source for how Google handles duplicate URLs and canonicalization.
  2. Google Search Central Useful for adjacent indexing controls and page directives that are often confused with canonicals.
  3. Moz Canonicalization Guide Clear practitioner-friendly overview of canonical tags and duplicate-content handling.
  4. Ahrefs Canonical Tags Guide Practical SEO explanation of implementation pitfalls and common use cases.
  5. Yoast SEO documentation Relevant because the query includes 'canonical yoast'; useful for WordPress implementation context.

Written and maintained by Nora Lindholm. Last updated 27 July 2026.

Spotted an error? Email me — corrections are logged and credited on the entry. Outbound links are unpaid; most are nofollow.