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Canonicalization & Duplicate Content

Brass-SEO · 3 entries · last verified August 2026

Brass-SEO tracks the canonicalization specifications because nearly every site creates duplicate URLs without meaning to — through URL parameters, www and non-www, HTTP and HTTPS, and tag or filter pages. The sources below are Google's own documentation and the IETF link-relation standard, and they explain how a site tells search engines which version of a page is the real one.

Contents — 3 entries
  1. 1.What Is URL Canonicalization
  2. 2.How to Specify a Canonical URL with rel=canonical and Other Methods
  3. 3.RFC 6596 — The Canonical Link Relation
  4. —Frequently Asked Questions

What Is URL Canonicalization

Google Search Central. Updated December 2025.

Brass-SEO draws on this for the single most important nuance about canonical tags: they are a request, not a command. Google states that 'indicating a canonical preference is a hint, not a rule,' and that 'Google may choose a different page as canonical than you do.' Google defines the canonical as 'the URL of a page that Google chose as the most representative from a set of duplicate pages' and uses it 'as the main source to evaluate content and quality.' Google also notes that 'some duplicate content on a site is normal and it's not a violation of Google's spam policies.' Brass-SEO uses this to reassure users that duplicates are a consolidation problem, not a penalty.

Examines:
Google's overview of how it selects a canonical URL, the signals it weighs, and its position that canonical declarations are hints rather than directives.
Brass-SEO draws on:
The 'hint, not a rule' framing and the 'duplicate content is not a spam violation' statement — cited when Brass-SEO explains why a canonical tag may be ignored and why duplicates are not a penalty.

How to Specify a Canonical URL with rel=canonical and Other Methods

Google Search Central. Updated March 2026.

Brass-SEO uses this as the how-to reference for declaring a canonical. Google lists several methods — redirects, the rel=canonical link element, a rel=canonical HTTP header, and sitemap inclusion — and notes that 'these methods can stack and thus become more effective when combined,' with redirects and rel=canonical treated as strong signals and sitemap inclusion as a weak one. Two practical rules Google states: the rel=canonical link element 'is only accepted if it appears in the head section,' and use absolute rather than relative paths. Google also prefers HTTPS over equivalent HTTP pages as canonical.

Examines:
Google's documented methods for specifying a canonical URL — redirects, link element, HTTP header, and sitemaps — with their relative strength and implementation rules.
Brass-SEO draws on:
The ranked list of canonicalization methods and the head-only and absolute-path rules — cited when Brass-SEO recommends how to consolidate duplicate URLs.

Frequently Asked Questions

Does duplicate content get a Google penalty?

Generally no. Google states that 'some duplicate content on a site is normal and it's not a violation of Google's spam policies.' The real issue with duplicates is consolidation, not punishment: Google picks one URL as canonical and concentrates its evaluation there, so without guidance it may choose a version you did not intend. Specifying a canonical URL helps Google consolidate signals on the page you want to rank.

Is a rel=canonical tag a command Google must follow?

No. Google is explicit that 'indicating a canonical preference is a hint, not a rule,' and that it 'may choose a different page as canonical than you do.' Google weighs your declared canonical alongside other signals — redirects, internal links, sitemap inclusion, and HTTPS preference. To make your preferred canonical more likely to win, align those signals rather than relying on the tag alone.

What are the ways to specify a canonical URL?

Google lists redirects, the rel=canonical link element (which is only accepted inside the page head), a rel=canonical HTTP header, and inclusion in a sitemap. Redirects and the rel=canonical element are strong signals; sitemap inclusion is a weak one. Google notes the methods can be combined for greater effect, and recommends absolute rather than relative paths.

Where does the canonical tag come from?

The rel=canonical link relation is defined by RFC 6596, an Informational IETF specification published in April 2012 by Maile Ohye and Joachim Kupke. It designates one URL as preferred over others with duplicative content and requires that the canonical target be duplicative of, or a superset of, the referring page. Because it is an open standard, major search engines support it rather than each having a proprietary tag.

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