February 20, 2025

Canonical Tag Malformed or Empty: How to Fix This Technical SEO Issue

by Brent D. Payne Founder/CEO
February 20, 2025
About Loud Led by industry veteran Brent D. Payne, who transformed digital strategies for Amazon and Groupon, Loud believes AI will revolutionize SEO.
Summary
Canonical tags play a crucial role in SEO by indicating the preferred version of a webpage to search engines. This guide explores the importance of canonical tags, how to identify and fix issues, and best practices for implementation to boost your site’s search visibility.

Understanding Canonical Tags and Their Importance

Canonical tags help consolidate ranking signals and avoid duplicate content.

What is a canonical tag and its purpose in SEO

Canonical tags are powerful tools in the SEO arsenal, serving as signposts for search engines to identify the primary version of a webpage when multiple similar URLs exist[1]. These HTML elements, appearing as <link rel=”canonical” href=”URL”/> in a page’s head section, play a critical role in preventing duplicate content issues and consolidating ranking signals to a preferred URL[2].

At Loud Interactive, we’ve seen firsthand how proper canonicalization can significantly impact a site’s search performance. By implementing canonical tags strategically, you can:

  1. Prevent search engines from wasting resources on crawling duplicate content
  2. Consolidate link equity and other ranking signals to the canonical version
  3. Ensure the correct URL appears in search results, especially for e-commerce sites with multiple product variants
  4. Optimize crawl budget by indicating which URL variants can be crawled less frequently[3]

How search engines interpret canonical tags

Search engines treat canonical tags as guidelines, verifying placement and URL accessibility.

Search engines employ sophisticated evaluation systems when processing canonical tags. They first verify the tag’s placement in the page’s <head> section, as tags in the body are ignored[1]. Multiple signals are then assessed to determine whether to honor the specified canonical URL, including:

  • Accessibility of the canonical URL (not returning 4xx/5xx errors)
  • Absence of robots.txt blocking
  • Proper implementation of hreflang clusters
  • Preference for HTTPS over HTTP versions[4]

It’s crucial to understand that while canonical tags provide a strong signal, search engines treat them as suggestions rather than directives. In cases of conflicting signals or implementation issues, search engines may choose to ignore the specified canonical and select what they determine to be the most appropriate version[2].

The impact of canonical tags on website rankings

Effective canonicalization consolidates ranking signals and streamlines site crawling.

Properly implemented canonical tags can significantly boost your website’s search rankings in several key ways:

  1. Consolidation of ranking signals from multiple duplicate URLs into a single preferred version
  2. Improved site structure and user experience
  3. More efficient crawling and indexing of content by search engines[5]

For optimal ranking benefits, we recommend combining canonical tags with consistent signals from other technical SEO elements like internal linking, sitemaps, and redirects. This approach is particularly valuable for e-commerce sites with product variations, content syndication, and sites dealing with URL parameters that could create duplicate content issues[6].

Identifying Malformed or Empty Canonical Tags

Implementation errors such as duplicate tags and syntax issues can nullify canonical benefits.

Common causes of malformed canonical tags

Through our experience at Loud Interactive, we’ve identified several common implementation errors that lead to malformed canonical tags:

  1. Incorrect URL protocol specification (using HTTP instead of HTTPS)
  2. Creation of canonical chains, where pages point to other pages with different canonical tags
  3. Syntax problems, such as using relative URLs instead of absolute URLs
  4. Pointing to URLs that return error status codes
  5. Accidental inclusion of multiple canonical declarations
  6. Placement of canonical tags in the page’s body instead of the head section[7][8]

Tools for detecting canonical tag issues

To ensure your canonical tags are functioning correctly, we recommend using a combination of tools:

  1. Google Search Console: Utilize the URL Inspection Tool for real-time analysis of individual pages and the Page Indexing report for identifying canonical-related issues affecting multiple pages[7].
  2. Specialized SEO platforms: These offer automated crawling capabilities to identify canonical problems at scale across your entire website[9].

Symptoms of empty or incorrect canonical tags

Identifying symptoms of problematic canonical tags is crucial for maintaining your site’s SEO health. Common indicators include:

  1. Pages appearing in Google Search Console’s ‘Duplicate without user-selected canonical’ report
  2. Search engines ignoring canonical tags due to issues like canonical chains or non-200 status codes
  3. Conflicting signals when canonical tags are combined with noindex directives or robots.txt blocks[7]

Fixing Malformed Canonical Tags: Step-by-Step Guide

Following a step-by-step approach to correct canonical tag syntax restores SEO effectiveness.

Correcting syntax errors in canonical tags

To fix malformed canonical tag syntax, follow these steps:

  1. Ensure proper placement in the HTML head section
  2. Use absolute URLs including the full domain path
  3. Maintain consistency in URL formatting (WWW or non-WWW, trailing slashes)
  4. Always use HTTPS if your site supports it
  5. Follow the correct syntax structure: <link rel="canonical" href="https://example.com/page.html"/>[11][12]

Avoid common errors such as using multiple canonical tags on a single page, pointing canonicals to redirected pages, and creating canonical chains[12].

Addressing dynamic canonical tag generation issues

Dynamic canonical tag generation requires careful implementation to avoid technical issues. To address these challenges:

  1. Ensure tags are included in the source HTML rather than injected via JavaScript
  2. Implement logic to consistently generate canonical tags pointing to the main product URL for e-commerce sites with variants
  3. Regularly monitor through crawling tools to identify problematic canonical chains or incorrect URL references
  4. Implement proper error handling and validation to prevent pointing to non-existent or problematic URLs[14]

Resolving conflicts between multiple canonical tags

When multiple canonical tags exist on a single page, follow these steps to resolve conflicts:

  1. Use SEO crawlers or Google Search Console to identify pages with competing canonical signals
  2. Analyze the HTML source code of affected pages to locate all canonical tag instances
  3. Choose the correct canonical URL by selecting the most authoritative version
  4. Remove redundant canonical tags by editing the HTML directly or updating CMS templates
  5. Verify that only one canonical tag remains in the page’s head section and points to the intended URL[16][17][18]

Implementing Best Practices for Canonical Tags

Adopt best practices like clean URLs and self-referencing tags to optimize SEO.

Choosing the correct canonical URL for each page

When selecting canonical URLs, prioritize versions that best serve users and search engines:

  1. Choose clean URLs without unnecessary parameters or tracking codes
  2. For e-commerce sites, designate the main product page URL as canonical
  3. Use HTTPS if available and maintain consistent use of www/non-www
  4. Implement self-referential canonicals even on primary pages
  5. For multilingual sites, each language version should have its own canonical URL[19][13]

Proper placement of canonical tags in HTML

Canonical tags must be placed in the <head> section of your HTML code to be properly recognized by search engines. The correct implementation looks like this: 

<link rel="canonical" href="https://example.com/page/" />

This placement is critical because search engines specifically look for canonical signals in the page’s head section when determining the preferred version of content to index[4][11].

Handling canonical tags across different page types

Different page types require specific canonical tag approaches:

  1. E-commerce sites with faceted navigation: Point canonical tags to main category/product pages
  2. Product pages under multiple categories: Specify one primary URL
  3. Paginated content: Use self-referencing canonicals or implement noindex tags
  4. Pages with UTM tracking parameters: Canonical to the clean URL version
  5. Multilingual sites: Implement proper hreflang annotations alongside canonical tags[21][11]

Monitoring and Maintaining Canonical Tag Health

Regular audits and performance tracking are essential for sustaining canonical tag accuracy.

Setting up regular canonical tag audits

To maintain proper technical SEO health, set up regular canonical tag audits:

  1. Use specialized crawling tools like Screaming Frog, Ahrefs, or Semrush for comprehensive site-wide checks
  2. Focus on identifying missing canonicals, broken canonical links, and conflicting tags
  3. Perform comprehensive audits every six months or after major site changes
  4. Implement monthly maintenance checks focused on critical canonical issues
  5. Monitor improvements through Google Search Console weekly[22][23]

Addressing canonical issues in site migrations

Thorough pre-migration audits and redirects are key to preserving canonical integrity.

During site migrations, carefully manage canonical tags to prevent SEO issues:

  1. Audit existing canonical tags before migration
  2. Ensure redirects are in place before updating canonical tags
  3. Verify that canonical tags point to new preferred URLs, not redirecting ones
  4. Avoid creating canonical chains
  5. Monitor Google Search Console for canonical-related issues post-migration[24]

Keeping canonical tags updated with content changes

Implement regular checks to ensure canonical tags remain aligned with current content revisions.

Maintain accurate canonical tags as content changes occur:

  1. Regularly monitor through crawling tools to catch issues from template modifications or content revisions
  2. Verify canonical tags remain correct through Google Search Console’s URL Inspection tool after content updates
  3. Implement validation checks for dynamic sites to prevent canonical tags from pointing to non-existent URLs
  4. Establish a content update workflow that includes checking canonical tag accuracy before publishing changes[25][2][4]
5 Key Takeaways
  1. Canonical tags are crucial for preventing duplicate content issues and consolidating ranking signals.
  2. Proper implementation in the HTML head section is essential for search engines to recognize canonical tags.
  3. Regular audits and monitoring are necessary to maintain canonical tag health and catch issues early.
  4. Different page types require specific canonical tag strategies to address their unique challenges.
  5. During site migrations and content changes, special attention must be paid to updating and verifying canonical tags.
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References
  1. [1] https://moz.com/learn/seo/canonicalization
  2. [2] https://ahrefs.com/blog/canonical-tags/
  3. [3] https://developers.google.com/search/docs/crawling-indexing/canonicalization
  4. [4] https://developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls
  5. [5] https://www.searchenginejournal.com/ranking-factors/canonicalization/
  6. [6] https://cognitiveseo.com/blog/19204/canonical-urls-seo/
  7. [7] https://seranking.com/blog/canonical-tag-issues/
  8. [8] https://developers.google.com/search/blog/2013/04/5-common-mistakes-with-relcanonical
  9. [9] https://sitebulb.com/hints/indexability/canonical-is-malformed-or-empty/
  10. [10] https://developers.google.com/search/docs/crawling-indexing/canonicalization-troubleshooting
  11. [11] https://surferseo.com/blog/canonical-tags-in-seo/
  12. [12] https://sitechecker.pro/site-audit-issues/canonical-is-missing/
  13. [13] https://www.semrush.com/blog/canonical-url-guide/
  14. [14] https://sitebulb.com/resources/guides/full-guide-to-the-canonical-tag/
  15. [15] https://www.greenlanemarketing.com/resources/articles/how-to-audit-your-canonical-tags
  16. [16] https://loud.us/post/multiple-canonical-tags/
  17. [17] https://sitechecker.pro/site-audit-issues/pages-multiple-canonical-urls/
  18. [18] https://reliqus.com/guide-to-fixing-canonical-issues-in-seo/
  19. [19] https://victorious.com/blog/guide-to-canonical-tags/
  20. [20] https://backlinko.com/canonical-url-guide
  21. [21] https://seranking.com/blog/canonical-tag-guide/
  22. [22] https://www.shopify.com/blog/technical-seo-audit
  23. [23] https://www.seoclarity.net/blog/audit-canonical-tags-in-two-steps
  24. [24] https://www.authoritylabs.com/solving-canonical-problems/
  25. [25] https://www.positional.com/blog/canonical-url
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