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Canonicalisation and Content Duplication – How it actually works in SEO?

Wilson Tiong

Content duplication is a common challenge nowadays with the abundance of new content and AI, often leading to SEO complications. Canonicalisation offers a solution, guiding search engines to the “preferred” version of a page.

This blog goes deep into the intricacies of both concepts.

Understanding Content Duplication

Understanding Content Duplication

Duplicate content is a prevalent issue in SEO, where identical or strikingly similar content appears across multiple URLs. This redundancy can confuse search engines about which version to index or rank for query results.

Let’s explore the common causes of this problem:

  • URL Variations: Even slight changes in a URL can lead to content duplication. For instance:
    • Trailing Slashes: The difference between and might seem trivial, but to search engines, these are distinct URLs with the same content.
    • URL Parameters: E-commerce sites often use parameters for tracking, filtering, or sorting products. For example, and might display similar products with slight variations.
  • HTTP vs. HTTPS and WWW vs. non-WWW: Websites accessible through both http:// and https:// or with and without the “www” prefix can inadvertently produce duplicate content. It’s essential to choose a preferred version and consistently use it.
  • Session IDs: Some websites generate unique session IDs for visitors, leading to URLs like This can result in numerous URLs with identical content.
  • Printer-friendly Pages: To enhance user experience, sites might offer “printer-friendly” versions of their articles. If these versions have separate URLs, they can be seen as duplicates.
  • Product Variations in E-commerce Sites: Online stores often have separate pages for minor product variations, like color or size. While the product might differ slightly, the bulk of the content (description, reviews, specifications) remains the same.
  • Content Syndication: If you’re syndicating your content on other sites or platforms, it’s crucial to ensure those sites use a canonical tag pointing back to the original content on your site. This indicates to search engines where the original content resides.
  • Mirror Sites: Sometimes, for reasons like load distribution, websites might have mirror sites hosting the same content. Without proper canonicalisation, this can be seen as duplication.

Implications of Duplicate Content

duplicate content

Duplicate content, while often unintentional, can have a range of adverse effects on a website’s SEO performance and user experience. Understanding these implications is crucial for webmasters and SEO professionals to prioritize addressing such issues. Here’s a detailed breakdown:

  • Search Engine Confusion: When multiple versions of a page exist, search engines face the dilemma of deciding which version is the most relevant to a given search query. This uncertainty can lead to:
    • Inconsistent Indexing: Search engines might choose to index only one version, and it might not always be the version you prefer.
    • Fluctuating Rankings: Different versions of the same content might bounce around in search results, leading to inconsistent visibility.
  • Diluted Content Authority: Each piece of content on your website can accumulate authority based on backlinks, user engagement, and other factors. When multiple duplicates exist:
    • Split Link Equity: Backlinks pointing to different versions of the same content can split the accumulated link equity, weakening the authority of each version.
    • Reduced User Engagement: Users might land on a less optimized or outdated version of your content, leading to lower engagement metrics like time on page or bounce rate.
  • Wasted Crawl Budget: Search engines allocate a specific crawl budget to each website, determining how many pages they’ll crawl in a given timeframe. Duplicate content can:
    • Consume Crawl Budget: Search engines might waste time crawling multiple identical pages, leaving less time for new or updated content.
    • Delay Content Discovery: New and important pages might take longer to be discovered and indexed if the crawl budget is exhausted on duplicates.
  • Potential for Duplicate Content Penalties: While search engines typically don’t penalize sites for unintentional duplication, blatant attempts to manipulate rankings or deceive users (like creating multiple domains with identical content) can lead to penalties.
  • User Experience Concerns: Beyond SEO, duplicate content can harm user experience. For instance:
    • Confusion: Users might bookmark or share a version of a page, only to find a different version later.
    • Inconsistent Information: If duplicates aren’t updated simultaneously, users might encounter outdated or conflicting information.
  • Loss of Valuable Traffic: If a less optimized or non-canonical version of your content ranks in search results, you might miss out on potential traffic. Users might not find the information they’re looking for or might encounter a page without the latest updates or user-friendly features.

Given these implications, it’s clear that addressing duplicate content should be a priority.

Enter, canonicalisation.

By designating a preferred or “canonical” version of a webpage, webmasters can guide search engines to the most authoritative and relevant version, ensuring that multiple similar pages don’t compete against each other in search rankings.

What is Canonicalisation?

canonical tag

At its core, canonicalisation is the process of selecting the best URL when there are several choices.

It’s a tool for webmasters to prevent self-competition and content dilution by designating a “canonical” or “preferred” URL among duplicates.

  • The Canonical Tag (`rel=”canonical”)

    • Function: The canonical tag is an HTML element that specifies the “master” copy of a webpage. By implementing this tag, webmasters can tell search engines which version of a page to index and rank.
    • Placement: This tag is placed in the <head> section of a webpage and points to the canonical version of that page.
    • Example: If and have the same content, you’d place <link rel=”canonical” href=”” /> in the <head> of both pages to indicate the former as the canonical version.
  • Cross-Domain Canonical Tags

    • Sometimes, the same content might exist across multiple domains. In such cases, you can use the canonical tag to point to the preferred domain.The process remains the same; the canonical tag on the duplicate domain’s page will point to the preferred page on the primary domain.

How to choose the Canonical Version to use?

choosing canonical version

The canonical version should be the most comprehensive, authoritative, and user-friendly version of the content.

It’s the URL you want users to see and search engines to index.

  • Consistency – Make sure that the canonical version is consistent across the site. For instance, if you choose the ‘www’ version of your site as canonical, all canonical tags should point to ‘www’ URLs.
  • XML Sitemap – Ensure that only canonical URLs are included in the XML sitemap. Avoid adding duplicate or non-canonical URLs.

No, It is not a Redirect.

It’s crucial to understand that canonicalisation is not the same as redirection. While both address duplicate content issues, a canonical tag is a signal to search engines, whereas a redirect (like a 301) physically sends users from one URL to another.


final thoughts on what is canonical and it's application

Addressing duplicate content is a piece of the larger SEO puzzle. It’s intertwined with other aspects like site architecture, backlink strategy, and content quality. A holistic approach ensures that all these elements work in harmony.

Ultimately, the goal is to offer high-quality, authoritative content to users. By addressing duplication and implementing canonicalisation correctly, you’re reinforcing your commitment to delivering a seamless and valuable user experience.

At ADEL SEO, we pride ourselves on being at the forefront of SEO knowledge, ensuring our strategies are always up-to-date and effective. If you’re looking for an agency in Adelaide who understands the nuances of SEO, from canonicalisation to content strategy and beyond, contact us!