Every marketer knows how important technical aspects are to your website’s discoverability. A key component of your technical SEO optimization is the canonical URL. The canonical URL prevents duplicate content. Google prefers to see unique and valuable content on websites and therefore penalizes content that is very similar or exactly the same.
Of course, you want to avoid being penalized by Google for similar or identical pages, but sometimes it’s impossible to include unique content on every page. Think, for example, of pages used for advertising campaigns or pages on online stores. The canonical URL is the solution for this.
A canonical URL is an HTML element in the head of your page. When it’s not possible to avoid duplicate content, use a canonical URL. This HTML element, also known as the “ rel=canonical,” tells search engines which page is the original one. So the canonical URL is essentially a source citation for your page.
head
rel=canonical
As a result, only one of the pages appears in the search results, and the search engine does not flag similar pages as duplicate content.
You use a canonical URL to prevent duplicate content. Search engines place great importance on the canonical URL. Although they can choose to ignore the canonical URL, the likelihood of them doing so is very low. The canonical URL tells search engines which page to index and which page is the source of the content.
It gives you the opportunity to provide search engines with guidelines, which gives you some control over which URLs appear in the search results. Plus, it prevents you from being penalized for duplicate content.
The canonical URL is useful for both internal and external duplicate content. Internal duplicate content is content on your website that is similar or identical. External duplicate content is content on your website that is similar or identical to content on other websites. You’re probably trying to avoid this, but sometimes it’s unavoidable—such as with landing pages for advertising campaigns.
Suppose you have two pages that are identical. For example: https://smartranking.nl/seo-specialisten/ and https://smartranking.nl/over-ons/seo-specialisten/.
So which page will be the source URL for your canonical tag? You know you have to choose, because duplicate content is penalized. If there’s any difference, you should obviously choose the most important and best page. Are they identical? Then, in principle, it doesn’t matter.
You can choose either the URL that gets the most visitors or the page with the cleanest URL. But in most cases, when the pages are identical, it doesn’t matter which URL you choose.
The canonical URL is an HTML element that you place in a page’s source code or in the HTTP header. You specify the canonical URL using the rel=canonical tag.
Visitors to your website won’t see this code and can therefore visit all pages with a canonical URL, while search engines know that there are similar versions of the page, ensuring that only one page is indexed.
The notation of the canonical URL in your page’s source code differs from the notation in the page’s HTTP header. In most cases, a canonical URL is specified in the page’s source code because it is easier to implement.
In the previous example, there are two similar pages, and we have chosen the page https://smartranking.nl/seo-specialisten/. You should then place the canonical URL in the source code for both pages as follows. Do this in the ` ` section. It looks like this:
A canonical URL is almost exclusively set in the HTTP header when there is duplicate content in the form of files such as a PDF. Sometimes, a PDF file contains similar or identical content.
Please note, however, that Google is the only search engine that supports this method of canonical URLs. The HTTP header syntax looks like this:
HTTP/1.1 200 OK Server: nginx Date: Wed, 27 Feb 2018 09:12:17 GMT Content-Type: application/pdf Content-Length: 1657 Last-Modified: Thu, 29 feb 2018 14:15:50 GMT Link: ; rel="canonical"
There are two types of canonical URLs: self-referencing canonical URLs and canonical URLs that link to another page.
We recommend placing a self-referencing canonical URL on every page. This may seem unnecessary, but it indicates that this is the only version of the page and that this version should be indexed.
When you use query parameters in the URL, a self-referencing canonical URL prevents Google from treating these different URLs as duplicate content. This is the case, for example, with marketing campaigns that use UTM tags, or with parameters in online store pages.
If you have multiple versions of a single page, add a rel=canonical tag that points to the correct version. For example, duplicate content can occur during an A/B test. It’s also possible that you’re using multiple pages for advertising campaigns or that you’ve copied an article and want to post it on your own website.
A common problem is duplicate content caused by having both a mobile and a desktop version of the website. Most websites are responsive these days, but this isn’t always the case. As a result, some websites have a separate mobile version. Visitors see the same content, but this content is loaded on different pages.
In this case, you should use a canonical URL, along with an alternate URL for the desktop version of your website. This helps you communicate the relationship between the different versions of your website. It also ensures that the search engine displays the correct version to the visitor. If the visitor is searching from a desktop, they’ll see the desktop version in the search results. Keep in mind, however, that only Google supports this implementation; other search engines, such as Bing, do not.
On the desktop version of your website, in addition to a canonical URL, you must include a rel="alternate" include the tag in the head at the bottom of the page, with a link to the mobile version of your website. It looks like this:
rel="alternate"
For the mobile version, include only the canonical URL, which looks like this:
In some cases, content is posted on multiple websites. This is often the case with publishers, among others. You’ll need to set a canonical URL for this as well. When your content is published on different pages—and therefore on different domains—you should use the cross-domain canonical tag. This lets search engines know the source of the content and which page should be indexed.
The canonical URL is important, so it’s crucial that you set it up correctly. There are a few things you can keep in mind to ensure the canonical URL is implemented correctly.
Always use the page’s absolute URL as the canonical URL. This is the fully qualified URL, including “https,” any subdomain, and the correct “www” notation.
In our case, we use https://smartranking.nl/blog/ for our blog page, not /blog/. This ensures that search engines know exactly which URL you’re referring to.
https://smartranking.nl/blog/
/blog/
For example, if your URL is accessible via both the WWW and non-WWW versions, you’ll still end up with duplicate content because search engines interpret the canonical URLs as https://smartranking.nl/blog/ and https://smartranking.nl/blog/.
https://smartranking.nl/blog/.
Always use only one canonical URL per page. Do not implement multiple canonical URLs in the source code or HTTP header. If there are multiple canonical URLs, search engines will become confused. Google ignores the canonical URL, even if multiple ones are present.
The canonical URL may only appear in the section of the page. If it is not included here, search engines will not find the canonical URL.
The page you’re linking to must be indexable. Otherwise, search engines will get confused if the canonical URL points to a page that has a 301 redirect, contains a ` noindex ` tag, or is otherwise not indexable.
noindex
You can help the search engine by making sure it includes the correct version of the URL in the sitemap. The URL in your sitemap must therefore be the same as your page’s canonical URL. In addition, the pages in the XML sitemap must be indexable.
There are a number of drawbacks to the canonical tag. For example, there is no evidence that a canonical tag actually passes on link equity. A link carries a certain amount of authority, which is a factor in your search result rankings.
Search engines are very unclear about whether or not this authority is passed on when a canonical tag is used. In principle, the canonical tag is designed to indicate which pages search engines should index.
Most SEO specialists are therefore convinced that the canonical tag only partially passes on authority. So be sure to keep this in mind when you’re actively working on your backlink profile and doing link building.
In addition, canonical tags do not prevent crawl issues. The canonical tag indicates which page is the source of the content, not which pages should be crawled. Crawling issues can arise, for example, from redirect loops or the indexability of useless pages. This eats up your crawl budget. You can prevent crawling issues by using the robots.txt file correctly.
Ultimately, it’s not always necessary to have multiple versions of pages. Sometimes a 301 redirect is a smarter and better option than a canonical URL. Set up a 301 redirect for pages that are accessible via both HTTP and HTTPS or via different domains or subdomains. If you still encounter duplicate content despite the 301 redirect, be sure to set up a canonical URL.
There is no definitive answer to this question. It is believed that only a portion of the authority is passed on when a page has a canonical URL. What is certain, however, is that a canonical URL is not intended to pass on link authority; 301 redirects are intended for that purpose.
A canonical URL is essentially a guideline that you set. A search engine may therefore choose to ignore it. In 99% of cases, search engines will follow the guideline as intended.
No, a canonical URL is used to specify a preferred version of a page. In this case, multiple versions of the page are accessible to visitors, but only one version may be indexed by search engines.
A 301 redirect redirects both visitors and search engines from one URL to another. You use this for pages that you’ve deleted, for example.
If you don’t implement canonical tags correctly, it can cause problems with your website’s indexing. Although you need to be careful with canonical tags, we recommend always using them to indicate to search engines which pages contain the original content.
The major search engines— Google, Bing, and Yahoo—support the canonical tag.
We know from Google that they will ignore all canonical tags in that case. We don’t know how other search engines handle this. That’s why we recommend using just one canonical tag per page.
No, crawlers will still crawl all pages. A canonical tag indicates which page should be displayed in the search results. You can prevent pages from being crawled by excluding them via your robots.txt file.
For paginated pages on your website or online store, it’s a good idea to set a self-referencing canonical tag pointing to the paginated URL. For the page https://smartranking.nl/blog/?page=2, you would set a canonical tag pointing to https://smartranking.nl/blog/?page=2.
https://smartranking.nl/blog/?page=2
With a passion for SEO and an unmatched drive for results, Jarik Oosting is the driving force behind SmartRanking. With over 15 years of experience in the field, he has built an extensive body of knowledge spanning technical SEO to complex site migrations. As the founder of SmartRanking, he has assembled a team of like-minded SEO specialists who help businesses achieve sustainable online growth.
His academic background in information science at the University of Groningen, with a specialization in natural language processing, gives him a unique perspective on the world of SEO. For Jarik, it’s not just about visibility in search engines, it’s about sharing knowledge and guiding businesses toward sustainable online success. That mission also led him to write a Dutch book about GEO.