In a world full of duplicate pages, how does Google decide which one gets the spotlight? Allan Scott from Google’s“Dups” team recently shed light on this mystery during an episode of Search Off the Record. He revealed that Google evaluates about 40 signals to select the canonical URL—the main version of a page to index and show in your search results.

Canonicalization: The Solution to Duplicate Content

Duplicate content is a very known and common issue for websites, causing confusion for search engines and diluting your SEO efforts. Google addresses this with canonicalization, a process that designates one URL as the primary version.

While signals like rel=”canonical” tags, sitemaps, and 301 redirects are known factors, the full scope is broader than you might think.

Scott explained:

“I’m not sure what the exact number is right now because it goes up and down, but I suspect it’s somewhere in the neighborhood of 40.”

Key Signals for Canonical Selection

Some of the major signals Google uses include:

• Rel=”canonical” tags
• 301 redirects
• HTTPS vs. HTTP preference
• Sitemaps
• Internal linking structures
• URL length

Each signal carries varying weight, but strong signals like canonical tags and 301 redirects are paramount. However, when conflicting signals arise, Google’s system may revert to secondary signals, creating a balancing act in the selection process.

Best Practices for Canonicalization

To help Google identify your preferred canonical URLs, follow these best practices:

1. Use rel=”canonical” tags correctly:
   • Ensure tags point to valid, existing URLs.
   • Use absolute URLs to avoid confusion.
2. Set up 301 redirects to permanently moved content:
3. Redirect old URLs to the preferred canonical versions.
4. Ensure HTTPS versions are accessible:
5. Always use secure URLs and update internal links to match.
6. Submit sitemaps with preferred URLs:
7. Include only canonical URLs in XML sitemaps.
8. Maintain consistent internal linking:
9. Avoid linking to duplicate or non-canonical versions of your pages.

Common Canonicalization Pitfalls to Avoid

Here are mistakes that can confuse Google and hurt your SEO:

1. Conflicting or incorrect canonical tags:
   • Avoid pointing to non-existent or irrelevant pages.
   • Use one canonical tag per page.
2. Canonical chains or loops:
3. Ensure pages don’t point to other canonical URLs in a sequence or loop.
4. Noindex with canonical tags:
5. Using both sends mixed signals—choose one approach per page.
6. Pointing canonicals to redirected or noindex pages:
7. Canonical tags must point to indexable pages with a 200 status code.
8. Case sensitivity issues:
9. Inconsistent URL casing can create duplicate content problems.
10. Ignoring pagination or URL parameters:
11. For paginated content, point canonical tags to the “View All” version or the first page.

Key Takeaways

Google’s canonicalization process is complex, balancing approximately 40 signals to determine the best URL. Here’swhat you need to know:

• Rel=”canonical” tags and 301 redirects are among the most influential signals.
• Conflicting signals lead Google to rely on secondary indicators.
• Consistent implementation of canonicalization practices is crucial for improving crawling, indexing, and search visibility.

Avoid common pitfalls, and you’ll give Google the clarity it needs to choose your preferred URLs. While we may never know the full list of signals, understanding and optimizing the known ones can possibly give your site an edge in search rankings.

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