If you have a single page accessible by multiple URLs, or different pages with similar content (for example, a page with both a mobile and a desktop version), Google sees these as duplicate versions of the same page. Google will choose one URL as the canonical version and crawl that, and all other URLs will be considered duplicate URLs and crawled less often.
If you don't explicitly tell Google which URL is canonical, Google will make the choice for you, or might consider them both of equal weight, which might lead to unwanted behavior, as explained below in Why should I choose a canonical URL?
What is a canonical URL?
Why would I have similar/duplicate pages?
There are valid reasons why your site might have different URLs that point to the same page, or have duplicate or very similar pages at different URLs. Here are the most common:
- To support multiple device types:
https://example.com/news/koala-rampage https://m.example.com/news/koala-rampage https://amp.example.com/news/koala-rampage
- To enable dynamic URLs for things like search parameters or session IDs:
https://www.example.com/products?category=dresses&color=green https://example.com/dresses/cocktail?gclid=ABCD https://www.example.com/dresses/green/greendress.html
- If your blog system automatically saves multiple URLs as you position the same post under multiple sections.
- If your server is configured to serve the same content for www/non-www http/https variants:
http://example.com/green-dresses https://example.com/green-dresses http://www.example.com/green-dresses
- If content you provide on a blog for syndication to other sites is replicated in part or in full on those domains:
There are a number of reasons why you would want to explicitly choose a canonical page in a set of duplicate/similar pages:
- To specify which URL that you want people to see in search results. You might prefer people reach your green dresses product page via
- To consolidate link signals for similar or duplicate pages. It helps search engines to be able to consolidate the information they have for the individual URLs (such as links to them) into a single, preferred URL. This means that links from other sites to
http://example.com/dresses/cocktail?gclid=ABCDget consolidated with links to
- To simplify tracking metrics for a single product/topic. With a variety of URLs, it's more challenging to get consolidated metrics for a specific piece of content.
- To manage syndicated content. If you syndicate your content for publication on other domains, you want to consolidate page ranking to your preferred URL.
- To avoid spending crawling time on duplicate pages. You want Googlebot to get the most out of your site, so it's better for it to to spend time crawling new (or updated) pages on your site, rather than crawling the desktop and mobile versions of the same pages.
Which is my canonical URL, according to Google?
Use the URL Inspection tool to learn which page Google considers canonical. Note that even if you explicitly designate a canonical page, Google might choose a different canonical for various reasons, such as performance or content.
- Incorrectly marked language variants: If you have multiple websites that serve substantially the same content localized to different users around the world, be sure to follow our guidelines for localized sites.
- Incorrect canonical tags: Some content management systems (CMS) or CMS plugins can make incorrect use of canonicalization techniques to point to URLs on external websites. Check your content to see if this is the case. If your site is indicating an unexpected canonical URL preference, perhaps through incorrect use of
rel="canonical"or a 301 redirect, fix that issue directly.
- Misconfigured servers: Some hosting misconfigurations may cause unexpected cross-domain URL selection. For example:
- A server may be misconfigured to return content from a.com in response to a request for a URL on b.com
- Two unrelated web servers may return identical soft 404 pages that Google fails to identify as error pages.
- Malicious hacking: Some attacks on websites introduce code that returns an HTTP 301 redirect or inserts a cross-domain rel=”canonical” link element into the HTML
<head>or HTTP header, usually pointing to a URL hosting malicious or spammy content. In these cases our algorithms may select the malicious or spammy URL instead of the URL on the compromised website.
- A copycat website: In rare situations, our algorithm may select a URL from an external site that is hosting your content without your permission. If you believe that another site is duplicating your content in violation of copyright law, you may contact the site’s host to request removal. In addition, you can request that Google remove the infringing page from our search results by filing a request under the Digital Millennium Copyright Act.
There are a few different ways to specify the canonical page among a duplicate set, depending on your usage:
|General guidelines||Follow these guidelines for all canonicalization methods.|
|rel=canonical <link> tag||
Add a <link> tag in the code for all duplicate pages, pointing to the canonical page.
|rel=canonical HTTP header||
Send a rel=canonical header in your page response.
Specify your canonical pages in a sitemap.
|301 redirect||Use 301 redirects to tell Googlebot that a redirected URL is a better version than a given URL. Use this only when deprecating a duplicate page.|
|AMP variant||If one of your variants is an AMP page, you will need to follow the AMP guidelines to indicate the canonical page and AMP variant.|
While we encourage you to use any of these methods, none of them are required. If you don't indicate a canonical URL, we'll identify what we think is the best version or URL.
For all canonicalization methods, follow these general guidelines.
- Don't use the
robots.txtfile for canonicalization purposes.
- Don't use the URL removal tool for canonicalization: it removes all versions of a URL from search.
- Don't specify different URLs as canonical for the same page using the same or different canonicalization techniques (for example, don't specify one URL in a sitemap but a different URL for that same page using
- Don't use noindex as a means to prevent selection of a canonical page. This directive is intended to exclude the page from the index, not to manage the choice of a canonical page.
Do specify a canonical page when using hreflang tags. Specify a canonical page in same language, or the best possible substitute language if a canonical doesn't exist for the same language.
Do link to the canonical URL rather than a duplicate URL, when linking within your site. Linking consistently to the URL that you consider to be canonical helps Google understand your preference.
Google prefers HTTPS pages over equivalent HTTP pages as canonical, except when there are issues or conflicting signals such as the following:
- The HTTPS page has an invalid SSL certificate.
- The HTTPS page contains insecure dependencies (other than images).
- The HTTPS page redirects users to or through an HTTP page.
- The HTTPS page has a
rel="canonical"link to the HTTP page.
Although our systems prefer HTTPS pages over HTTP pages by default, you can ensure this behavior by taking any of the following actions:
- Add redirects from the HTTP page to the HTTPS page.
- Add a
rel="canonical"link from the HTTP page to the HTTPS page.
- Implement HSTS.
To prevent Google from incorrectly making the HTTP page canonical, you should avoid the following practices:
- Bad SSL certificates and HTTPS-to-HTTP redirects cause us to prefer HTTP very strongly. Implementing HSTS cannot override this strong preference.
- Including the HTTP page in your sitemap or hreflang entries rather than the HTTPS version.
- Implementing your SSL/TLS certificate for the wrong host-variant: for example, example.com serving the certificate for www.example.com. The certificate must match your complete site URL, or be a wildcard certificate that can be used for multiple subdomains on a domain.
Use Parameter Handling to tell Googlebot about any parameters that should be ignored when crawling. Ignoring certain parameters can reduce duplicate content in Google's index and make your site more crawlable. For example, if you specify that the parameter
sessionid should be ignored, Googlebot will consider the following two URLs as duplicates:
Choose one of the following methods to specify a canonical URL for duplicate URLs or duplicate/similar pages.
Be sure to follow the general guidelines above for all methods.
You can use a
<link> tag in the page header to indicate when a page is a duplicate of another page.
Suppose you want
https://example.com/dresses/green-dresses to be the canonical URL, even though a variety of URLs can access this content. Indicate this URL as canonical with these steps:
Mark all duplicate pages with a
rel="canonical"link element. Add a
<link>element with the attribute
<head>section of duplicate pages, pointing to the canonical page, like this one:
<link rel="canonical" href="https://example.com/dresses/green-dresses" />
If the canonical page has a mobile variant, add a
rel="alternate"link to it, pointing to the mobile version of the page:
<link rel="alternate" media="only screen and (max-width: 640px)" href="http://m.example.com/dresses/green-dresses">
Add any hreflang or other redirects appropriate for the page.
Use this structure:
Not this structure:
If you can configure your server, you can use
rel="canonical" HTTP headers (rather than HTML tags) to indicate the canonical URL for non-HTML documents such as PDF files.
For example, if you expose a PDF file through multiple URLs, you can return a
rel="canonical" HTTP header such as the following for the duplicate URLs to tell Googlebot what is the canonical URL for the PDF file:
Link: <http://www.example.com/downloads/white-paper.pdf>; rel="canonical"
Google currently supports this method for web search results only.
rel="canonical"link element. That is:
Use this structure:
Not this structure:
Use a sitemap
Pick a canonical URL for each of your pages and submit them in a sitemap. All pages listed in a sitemap are suggested as canonicals; Googlebot will decide which pages (if any) pages are duplicates, based on similarity of content.
We don't guarantee that we'll consider the sitemap URLs to be canonical, but it is a simple way of defining canonicals for a large site, and sitemaps are a useful way to tell Google which pages you consider most important on your site.
Don't include non-canonical pages in a sitemap. If using a sitemap, specify only canonical URLs in the sitemap.
Use 301 redirects for retired URLs
Use this method when you want to get rid of existing duplicate pages, but need to ensure a smooth transition before you retire the old URLs.
Suppose your page can be reached in multiple ways:
Pick one of those URLs as your canonical URL and use 301 redirects to send traffic from the other URLs to your preferred URL. A server-side 301 redirect is the best way to ensure that users and search engines are directed to the correct page. The 301 status code means that a page has permanently moved to a new location.
If you are on a website hosting service, do a search for their documentation on setting up 301 redirects.