How Google Uses 40 Signals to Determine Canonical URLs

Google evaluates approximately 40 different signals when deciding which version of a page to treat as the canonical version. This process is critical for search engines to avoid indexing duplicate content and ensure that the right page is recognised and ranked appropriately. These signals can include factors like internal linking, URL structure, and the presence of specific HTML tags.

Among these various signals, the most influential are canonical tags and redirects. Canonical tags explicitly tell Google which version of a page to consider as the primary one, while redirects (such as 301 redirects) guide users and search bots to the correct page. However, it’s important to understand that these signals can sometimes be overridden, particularly when there are conflicting elements within the page or site structure that confuse Google’s crawlers.

To ensure that Google correctly interprets the canonical version of your pages, it is recommended to consistently implement canonicalisation practices across your entire website. This means ensuring that canonical tags are correctly applied on all duplicate pages and maintaining a logical, clean URL structure. This consistent implementation helps guide search engines to the most relevant pages, ultimately improving your site’s indexing and SEO performance by preventing potential issues caused by duplicate content. By taking these steps, you can ensure that your content is properly understood and valued by search engines.

In a recent episode of Google’s Search Off the Record podcast, Allan Scott from the “Dups” team discussed how Google determines the main URL when faced with duplicate pages on a website. He explained that Google uses a variety of signals to make this decision.

According to Scott, Google evaluates approximately 40 different signals when selecting the most relevant URL from a set of duplicate pages. These signals play a crucial role in helping Google choose which page to index and rank higher, ensuring that the right content is prioritised in search results.

Around 40 Signals For Canonical URL Selection

Duplicate content is a common issue for search engines, as many websites often have multiple pages featuring the same or similar content. This can lead to confusion for search engines, making it difficult for them to determine which page should be considered the primary one.

To address this problem, Google employs a process called canonicalization. Through canonicalisation, Google selects one URL as the main version to index and display in search results. This ensures that the correct page is prioritised, avoiding penalties or dilution of search rankings due to duplicate content.

Google has emphasised the importance of using certain signals, such as the rel=”canonical” tag, sitemaps, and 301 redirects, in the canonicalisation process. However, it turns out that the number of signals Google uses to determine the canonical version of a page is greater than many website owners may expect.

During the podcast, Scott revealed, “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 neighbourhood of 40.” This indicates that Google takes a variety of signals into account when determining which URL to consider as the main version for a group of similar pages.

Some of the known signals mentioned by Scott include:

rel=”canonical” tags
301 redirects
HTTPS vs. HTTP
Sitemaps
Internal linking
URL length

It’s important to note that the weight and importance of each signal can vary. For instance, signals like rel=”canonical” tags play a crucial role, as they can influence both the clustering of pages and the canonicalisation process itself. This highlights the complexity of how Google determines which pages should be indexed and ranked.

Balancing Signals

With so many signals at play, Allan Scott acknowledged the challenges Google faces when determining the canonical URL, especially when signals conflict with each other.

He explained that in such cases, “If your signals conflict with each other, what’s going to happen is the system will start falling back on lesser signals.” This highlights that while strong signals like rel=”canonical” tags and 301 redirects play a significant role, they are not always the sole determining factors.

When these signals are unclear or contradictory, other signals may come into play. As a result, Google’s canonicalisation process becomes a delicate balancing act, where the system works to identify the most appropriate canonical URL based on the available signals.

Best Practices For Canonicalization

Clear signals play a crucial role in helping Google identify the preferred canonical URL for a page. To ensure this process works effectively, it’s essential to follow some best practices.

One key practice is to use rel=”canonical” tags correctly, as these directly inform Google of the preferred version of a page. Additionally, implementing 301 redirects for content that has been permanently moved is vital to guide Googlebot to the correct page.

Another important step is to make sure that the HTTPS versions of your pages are accessible and properly linked, ensuring secure browsing for both users and search engines. Submitting sitemaps with the preferred canonical URLs further enhances the chances of Google correctly identifying the right pages to index.

Finally, maintaining consistency in internal linking is essential for making sure Googlebot can easily follow the right paths across your site.

By following these best practices, you help Google find the correct canonical URLs, which in turn improves your site’s crawling, indexing, and overall visibility in search results.

Mistakes To Avoid

Here are some common mistakes to watch out for when managing canonical URLs:

Incorrect or conflicting canonical tags:
This can occur when canonical tags point to non-existent or 404 pages, or when there are multiple canonical tags with different URLs on the same page. Another issue is when the tag points to a completely different domain.
Fix: Double-check the canonical tags to ensure there is only one per page, and always use absolute URLs.
Canonical chains or loops:
A canonical chain or loop happens when Page A points to Page B as its canonical, but Page B in turn points back to Page A or to another page, creating a loop.
Fix: Make sure the canonical URLs always point to the final, preferred version of the page.
Using noindex and canonical tags together:
This creates confusion for search engines because “noindex” tells Google not to index the page at all, making the canonical tag redundant.
Fix: Use canonical tags to consolidate similar pages and use “noindex” for exclusion.
Canonicalising to redirected or noindex pages:
When canonical tags point to pages that are either redirected or marked with “noindex”, it confuses search engines.
Fix: Ensure that canonical URLs point to pages with a 200 status and are indexable.
Ignoring case sensitivity:
Inconsistent casing in URLs can lead to duplicate content issues, as search engines treat differently cased URLs as separate pages.
Fix: Maintain consistent casing for both URLs and canonical tags.
Overlooking pagination and parameters:
Paginated content and URLs with multiple parameters can cause duplication issues if they are not managed properly.
Fix: Use canonical tags pointing to the first page or a “View All” page for paginated content, and keep URL parameters consistent across your site.

By addressing these common issues, you can avoid problems with canonicalisation and ensure your site is optimised for search engines.

Key Takeaways

It’s unlikely that the full list of over 40 signals Google uses to determine canonical URLs will ever be publicly disclosed. However, the recent discussion provided valuable insights worth noting.

Here are the key takeaways:

Google uses around 40 different signals to decide which URL should be considered canonical, with strong indicators such as rel=”canonical” tags and 301 redirects playing a major role.
In cases where signals conflict, Google relies on secondary signals to help determine the correct canonical URL.
A clear and consistent implementation of canonicalisation signals — including tags, redirects, sitemaps, and internal linking — is essential for guiding search engines.
Common mistakes, such as canonical chains, mixed signals, or incorrect implementations, can lead to confusion for search engines, impacting the effectiveness of canonicalisation.

By keeping these points in mind, you can ensure better optimisation of your site’s canonicalisation strategy.

The complete list of over 40 signals that Google uses to determine canonical URLs is unlikely to be made publicly available. However, the recent insights shared about this process offer some valuable takeaways for webmasters and SEO professionals.

Firstly, Google considers around 40 different signals when deciding which URL should be treated as canonical. Among the most influential signals are rel=”canonical” tags and 301 redirects, both of which play a crucial role in guiding Google’s decision-making process.

In situations where these signals conflict with one another, Google tends to rely on secondary signals to determine the preferred canonical URL. This highlights the importance of having a comprehensive strategy for implementing canonical signals across your site.

To ensure search engines correctly identify the canonical version of a page, it’s important to maintain clear and consistent use of canonicalisation signals, such as rel=”canonical” tags, 301 redirects, sitemaps, and internal linking structures. This consistency is key to avoiding confusion.

Additionally, common mistakes like creating canonical chains, sending mixed signals, or making incorrect implementations can cause confusion for search engines, ultimately affecting the success of your canonicalisation efforts.

By following these best practices and keeping these points in mind, you can help optimise your site’s canonicalisation strategy and improve its visibility in search results.