Rel canonical is a subject often missed in SEO circles, but in reality, these hold mighty power. It’s not just an HTML code; instead, it’s the silent driver of page authority, the search directive that distinguishes a topical page from duplicate pages.
Let’s dive into it to understand what it is and why it’s important in SEO.
What is a Canonical URL?
A canonical URL is a URL belonging to the primary page (or the topical page) from a set of duplicate pages or similar URLs. It is used to identify which page is most representative of a topic and should be indexed by search engines.
For example, if multiple URLs on a website contain similar content, one of them would be the preferred or “official” URL that you want search engines to crawl for indexing and ranking. This is the canonical URL.
Specifying a canonical URL to search engines helps consolidate link equity across duplicate pages, eventually delivering page rank where it’s due. In addition, it prevents crawler confusion and weakened search ranking signals.
What is a canonical URL example?
Here’s an example to understand this better. This is a product category page for laptops on an e-commerce site:
https://www.mysite.com/product/laptops
But the site has other versions of the same page. These are for when a user decides to add filters to the page to narrow down their choices:
https://www.mysite.com/product/laptops?brand=dell
https://www.mysite.com/product/laptops?ram=16gb
Or another version created for when the same page is opened using a link from Instagram.
https://www.mysite.com/product/laptops?ref=instagram
As the attributes change, things keep piling up on the same URL leading to multiple versions of the same page. So, how do we inform search engines of the original version of the page? We add a rel canonical tag to the rest of the pages and a self-referential tag to the canonical URL.
The Role of Rel Canonical?
Rel canonical is a link element inserted into the HTML code snippet to highlight that another page is most representative of that page’s content. This tag is placed in the <head> section of webpages to point search engines to the master version of a page series. Here’s what a canonical tag looks like.
The rel=”canonical” tag indicates which page is to be indexed and which ones are to be ignored or kept in the back burner. It helps ensure appropriate canonicalization, mitigating issues that may arise with duplicate content.
Where is this tag placed?
In order to define a canonical URL, you need to have a rel canonical tag on every page that’s identical to the main page. It’s placed in the <head> section of HTML code belonging to duplicate pages. This way, any similar pages will point to the main URL, consolidating it as the preferred page for indexation.
Take this, for instance. A Redditor perfectly explained canonical tags with a rather layperson example.
“You are dating a girl named Sally. She has 3 identical twin sisters. You can’t distinguish them from each other. So they all wear t-shirts with an arrow pointing to Sally. Sally wears a t-shirt saying “I’m Sally”.”
Why is Sally wearing a shirt saying “I’m Sally”? Because the master page also needs a self-referential tag pointing to itself. John Mueller emphasized this in a previous Google Webmaster Central hangout.
Why Rel Canonical Tag Is Important for SEO?
Because rel canonical tag strengthens your SEO signals by addressing duplication issues and redirecting authority to the primary URL.
Suppose your website has a product page for an electric scooter. This electric scooter is available in three different colors. Naturally, there would be URL parameters designated to serve each variation. But these variations can confuse Google crawlers about which page to display in the search engine results pages.
Google crawlers are designed to group pages and URLs that look similar. This means any URLs having:
- Multiple UTM parameters
- Live staging URLs
- Two versions (HTTP or HTTPs)
- Separate URLs for mobile and desktop versions
- Product page variations with filters or sorting options
- URLs specified for different locations (www.mysite.com/us and www.mysite.com/uk)
This can lead to Google canonicalization issues, as crawlers will automatically pick a page to index. If that page isn’t your preferred source for search engines, it’ll lead to:
- Wasted crawl budget
- Diluted link equity (PA affected for primary page)
- Decreased ranking potential
So, in case your website fits into any of the scenarios above, implementing canonicalization is critical. Why do we use rel canonical tags again? To put it simply, it ensures you’re sending strong signals to Google about the canonical page.
The rel=”canonical” tag, when appropriately applied alongside other relevant factors like 301 redirects, an appropriate sitemap, powerful internal linking, hreflang tags, and an HTTPS server, will assist in the identification of the correct canonical URL.
Why Implement Rel Canonical Tags?
Because there are many things that can go wrong if you don’t. For starters,
- Google might automatically select a page you don’t want as your canonical page.
- All page authority and link juice will be transferred to that page.
- Your main page will be considered a duplicate.
But appropriate canonical tags can send signals clearly implying that “this is the main page, index this.” So, that’ll fix the first part of the equation. But that’s not where the benefits of rel canonical end. It also:
Retains Crawl Budget
The issue of crawl budget rarely arises with smaller sites, but it is a common occurrence for sites with thousands of URLs. Since these websites already have a huge crawl load, they can’t afford to lose crawl resources to improper canonicalization. That’s where canonical tags sweep in. By redirecting search crawlers to the main page, they effectively save up on wasted crawl budget.
Supports Discovery of Important Content
Saving crawl budget means crawlers spend more time and resources looking for important content on your websites. This means that all other topical pages are discovered and indexed with no content of value getting missed or overlooked.
Strengthens Ranking Signals
Too many duplicate pages can dilute authority, splitting it across different sections of a website. Canonicalization resolves this issue and ensures that link equity is delivered to the single, most important page.
Ensures Correct URLs get Ranked:
Google specifies in its blog that its system identifies canonical pages better when multiple methods are stacked and used in conjunction. For example, if you apply rel canonical tag but also specify the canonical URL in your sitemap, it improves the chances of the correct page getting indexed and displayed in the SERPs.
Better User Experience
With better visibility of a canonical page on the SERPs, users land where they’re supposed to. Not some duplicate version of the page with filters or unrequired parameters attached. This improves the overall user experience of a website.
Ways To Implement Rel Canonical Tag & URL
John Mueller said Google uses two ways to identify which page should be indexed, granted it has duplicate pages.
- Sites’ Preferences
- User Preferences
And a site can identify its preferences in multiple ways, for example:
Inserting Rel Canonical Annotation
Remember, the most powerful signal to identify a canonical URL is the rel=”canonical” annotation in the head section of a URL. It’s simple and helpful in redirecting search engines to key pages on a website, helping avoid redistribution of credibility across a series of thin pages.
Also, it’s pretty simple to implement this tag manually. Just add the <link rel=”canonical” tag pointing to the preferred page in the head section of all existing duplicates of a page. Just like we did in the example below, where our blog page was the preferred source:
<link rel=”canonical” href=”https://www.linkbuildinghq.com/blog/”>
Avoid combining two different annotations in one URL, as your canonical will probably get ignored in that case.
Using A Plugin
Manual entry is effective, but it can be time-consuming. Yet WordPress plugins have solved this problem. Many plugins are designed to automatically implement rel canonical, so your site doesn’t run into duplication issues. Yoast SEO, Rank Math, and All in One SEO are the most popular plugins for this purpose.
Moreover, the Wix Editor also assists canonicalization by adding self-referential canonical tags to each page on a website. You can customize tags on a case-by-case basis as well, ensuring precision and removing technical errors in the automated process.
Using HTTP Header
This is a method reserved for non-HTML pages like PDFs, Microsoft Word docs, or other formats. Since these pages do not have a <head> section, you can’t add the rel canonical tag there. However, you can still specify a canonical URL for such pages.
For that, you’ll need access to the .htaccess file of the website. There, you can insert the rel canonical link element in the following format:
Link: <https://www.linkbuildinghq.com/document.pdf>; rel=”canonical”
Identify Canonical Page in Your Sitemap
Google assumes that all URLs listed on your sitemap are the master versions. And that gives you another way to specify your canonical URLs. It’s easy; just list them all on your sitemap, and that’s it! That’s basically all you have to do.
But this method works best when combined with other canonical signals like 301 redirects or rel canonical tags.
Setting Up 301 Redirects
A 301 redirect basically shifts users from one URL to another. In essence, this is a strong signal for Google, as it recognizes the redirected page as canonical. But you can’t use this as your primary method to specify canonical URLs to Google.
Bear in mind that a 301 replaces the URL, whereas a canonical tag clarifies your preferences while keeping the duplicate page accessible. So, using a 301 redirect is recommended only when:
- You wish to remove duplicate URLs (and consolidate link equity from outdated pages into a new one)
- When the site goes through major restructures
- Shifting from HTTP to HTTPS
Point to note:
Overdoing 301 redirects can be risky, as applying too many of these can increase load time and result in wasted crawl budget
Apply Hreflang Annotation
Hreflang tags should be part of a site’s canonicalization campaign if the site operates in multiple locations and has region-specific versions of the main URL. Google mentions in their blog.
“To help with sites’ localization efforts, for canonicalization purposes Google prefers URLs that are part of hreflang clusters.”
Essentially, clustered regional URLs (those pointing to each other) are preferred when Google is analyzing URLs for canonicalization. For example, if URL A and URL B mutually point to each other, but they don’t point to URL C, the first two URLs will be considered canonicals instead of the third one, as it isn’t part of a cluster.
To specify regional alternates of a page, use the link annotation link rel=”alternate” hreflang. Make sure not to combine hreflang annotations with rel canonical, as “rel=”canonical” annotations that suggest alternate versions of a page are ignored.”
Common Mistakes with Rel Canonical Link Tag
Rel canonical tag seems pretty simple, but it can be a bit tricky. Any errors or misconfigurations are often not very clear and may result in the canonical URL not getting recognized efficiently. Below are the most common rel canonical mistakes we’ve witnessed so far.
- Component pages do not need a rel canonical. For example, if an article of your website spans multiple pages, applying a rel canonical tag on page 2, 3, and more of that series is not correct. In this case, re=”next” and rel=”prev” markup is more suitable.
- Specifying relative URLs instead of absolute URLs in the link <link> tag. For a canonical tag to be recognized and applied effectively, you need to use an absolute tag—one that specifies the full path of a URL, including the https:// section. For example: ✅ <link rel=canonical href=”https:example.com/laptop.html” /> ❎ <link rel=canonical href=”example.com/laptop.html” />
- Not verifying if the automated rel canonical tags inserted via SEO plugins are done correctly. In many cases, this can lead to pages containing multiple rel canonical links to different URLs.
- Copying a page’s template without removing or changing the rel canonical target that was already present. This can lead to the site owner’s page specifying the template’s page as a canonical URL.
- When a category or landing page contains rel canonical tag for a featured article. Even if your category page contains very similar content to the article, implementing a canonical tag on a category landing page pointing to an article will essentially cause the landing page to disappear from search results.
- Inserting the rel canonical link tag into the <body> instead of the <head> section. Google claims that “When we encounter a rel=canonical designation in the <body>, it’s disregarded.”
Canonical URL Best Practices
To make sure you’re not making any mistakes while applying the rel canonical tag, refer to the best practices for canonicalization.
- Ensure all duplicate or alternate versions of a page point to the same preferred (canonical) URL.
- Make sure that your canonical URL contains a large portion of the content available on its duplicate page.
- Add only one canonical tag per page, and place it high in the <head> section so search engines can find it easily.
- Always point your canonical tag to a clean, working, indexable URL, and avoid broken pages, blocked URLs, or fragments.
- Use self-referencing canonicals in which a page points to itself to indicate it’s the preferred version.
- Keep everything consistent — your rel canonical link attribute, internal links, and sitemap should all point to the same canonical URLs.
- Avoid sending mixed signals like:
- Creating circular canonicals (A points to B, and B points back to A).
- Using canonical chains (A → B → C).
- Specifying different canonicals in different places (like one in your sitemap and another in the page tag).
- Don’t rely on robots.txt, the URL removal tool, or noindex to handle canonicalization. Nor should you use multiple alternate link attributes along with a rel canonical tag as it can confuse crawlers.
- For JavaScript-heavy websites, set the canonical URL in the HTML source code and avoid changing it dynamically with scripts. If you can’t place it in the source code, leave it out and set it with JavaScript.
- If you manage multiple websites with similar content, use cross-domain rel canonical tags strategically to consolidate ranking signals.
- Test your canonical setup regularly using SEO tools to confirm search engines are recognizing the correct version
