How to specify a canonical URL with rel="canonical" and other methods
To specify a canonical URL for duplicate or very similar pages to Google Search, you can indicate your preference using a number of methods. These are, in order of how strongly they can influence canonicalization:
- Redirects: A strong signal that the target of the redirect should become canonical.
-
rel="canonical"
link
annotations: A strong signal that the specified URL should become canonical. - Sitemap inclusion: A weak signal that helps the URLs that are included in a sitemap become canonical.
Keep in mind that these methods can stack and thus become more effective when combined. This means that when you use two or more of the methods, that will increase the chance of your preferred canonical URL appearing in search results.
While we encourage you to use these methods, none of them are required; your site will likely do just fine without specifying a canonical preference. That's because if you don't specify a canonical URL, Google will identify which version of the URL is objectively the best version to show to users in Search.
Reasons to specify a canonical URL
While it's generally not critical to specify a canonical preference for your URLs, there are a number of reasons why you would want to explicitly tell Google about a canonical page in a set of duplicate or similar pages:
-
To specify which URL that you want people to see in search results.
You might prefer people to reach your green dresses product page through
https://www.example.com/dresses/green/greendress.html
rather thanhttps://example.com/dresses/cocktail?gclid=ABCD
. -
To consolidate signals for similar or duplicate pages. It helps
search engines to be able to consolidate the signals they have for the individual
URLs (such as links to them) into a single, preferred URL. This means that signals
from other sites to
https://example.com/dresses/cocktail?gclid=ABCD
get consolidated with links tohttps://www.example.com/dresses/green/greendress.html
if the latter becomes canonical. - To simplify tracking metrics for a piece of content. With a variety of URLs, it can be more challenging for you to get consolidated metrics for a specific piece of content.
- To avoid spending crawling time on duplicate pages. You may want Googlebot to get the most out of your site, so it's better for it to spend time crawling new (or updated) pages on your site, rather than crawling duplicate versions of the same content.
Best practices
For all canonicalization methods, follow these best practices:
- Don't use the robots.txt file for canonicalization purposes.
- Don't use the URL removal tool for canonicalization. It hides all versions of a URL from Search.
-
Don't specify different URLs as canonical for the same page using
different canonicalization techniques (for example, don't specify one URL in a
sitemap, but a different URL for that same page using
rel="canonical"
). - Don't specify a fragment URL as canonical, as Google generally doesn't support fragment URLs.
-
We don't recommend using
noindex
to prevent selection of a canonical page within a single site, because it will completely block the page from Search.rel="canonical"
link
annotations are the preferred solution. -
If you're using
hreflang
elements, make sure to specify a canonical page in the same language, or the best possible substitute language if a canonical page doesn't exist for the same language. - When linking within your site, link to the canonical URL rather than a duplicate URL. Linking consistently to the URL that you consider to be canonical helps Google understand your preference.
Comparison of canonicalization methods
The following table compares the different canonicalization methods, highlighting their strengths and weaknesses when it comes to maintenance and efficacy in different scenarios.
Method and description | |||
---|---|---|---|
rel="canonical" link element
|
Add a
|
||
rel="canonical" HTTP header
|
Send a
|
||
Sitemap |
Specify your canonical pages in a sitemap.
|
||
Redirects | Use 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, follow the AMP guidelines to indicate the canonical page and AMP variant. |
Use rel="canonical"
link
annotations
Google supports explicit rel
canonical link
annotations as described in
RFC 6596.
rel="canonical"
annotations that suggest alternate versions of a page are ignored;
specifically, rel="canonical"
annotations with hreflang
,
lang
, media
, and type
attributes are not used for
canonicalization. Instead, use the appropriate link
annotations to specify alternate
versions of a page; for example, link
rel="alternate"
hreflang
for
language and country annotations.
You can provide the rel="canonical"
link
annotations in
two ways:
We recommend that you choose one of these and go with that; while supported, using
both methods at the same time is more error prone (for example, you might provide
one URL in the HTTP header, and another URL in the rel="canonical"
link
element).
The rel="canonical"
link
element
A rel="canonical"
link
element (also known as a
canonical element) is an element used in the head
section of HTML
to indicate that another page is representative of the content on the 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:
-
Add a
<link>
element with the attributerel="canonical"
to the<head>
section of duplicate pages, pointing to the canonical page. For example:<html> <head> <title>Explore the world of dresses</title> <link rel="canonical" href="https://example.com/dresses/green-dresses" /> <!-- other elements --> </head> <!-- rest of the HTML -->
-
If the canonical page has a mobile variant on a separate URL, add a
rel="alternate"
link
element to it, pointing to the mobile version of the page:<html> <head> <title>Explore the world of dresses</title> <link rel="alternate" media="only screen and (max-width: 640px)" href="https://m.example.com/dresses/green-dresses"> <link rel="canonical" href="https://example.com/dresses/green-dresses" /> <!-- other elements --> </head> <!-- rest of the HTML -->
-
Add any
hreflang
or other elements that are appropriate for the page.
Use absolute paths rather than relative paths with the rel="canonical"
link
element. Even though relative paths are supported by Google, they
can cause problems in the long run (for example, if you unintentionally allow your
testing site to be crawled) and thus we don't recommend them.
Good example:
https://www.example.com/dresses/green/greendress.html
Bad example:
/dresses/green/greendress.html
The rel="canonical"
link element
is only accepted if it
appears in the <head>
section of the HTML, so make sure at least the
<head>
section is valid HTML.
If you use JavaScript to add the rel="canonical"
link
element,
make sure to
inject the canonical link element properly.
The rel="canonical"
HTTP header
If you can change the configuration of your server, you can use a link
HTTP response header
with a rel="canonical"
target attribute as defined by
RFC5988
rather than an HTML element to indicate the canonical URL for a document supported
by Search, including non-HTML documents such as PDF files.
Google supports this method for web search results only.
If you publish content in many file formats, such as PDF or Microsoft Word, each on
their own URL, you can return a rel="canonical"
HTTP header to tell
Googlebot what is the canonical URL for the non-HTML files. For example, to indicate
that the PDF version of the .docx
version should be canonical, you might
add this HTTP header for the .docx
version of the content:
HTTP/1.1 200 OK Content-Length: 19 ... Link: <https://www.example.com/downloads/white-paper.pdf>; rel="canonical" ...
As with the rel="canonical"
link
element, use absolute URLs
in the rel="canonical"
HTTP header, and as per
RFC2616,
use only double quotes around the URL.
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; Google will decide which pages (if any) are duplicates, based on similarity of content.
Supplying the preferred canonical URLs in the sitemaps 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.
Use redirects
Use this method when you want to get rid of existing duplicate pages. All
redirection methods
—301
and 302
redirects, meta-refresh
,
JavaScript redirects—have the same effect on Google Search, however the time
it takes for search engines to notice the different redirect methods may differ.
For the quickest effect, use 3xx
HTTP (also known as server-side)
redirects.
Suppose your page can be reached in multiple ways:
https://example.com/home
https://home.example.com
https://www.example.com
Pick one of those URLs as your canonical URL, and use redirects to send traffic from the other URLs to your preferred URL.
Other signals
Apart from explicitly provided methods, Google also uses a set of canonicalization signals
that are generally based on site setup: preferring HTTPS over HTTP, and URLs in
hreflang
clusters.
Prefer HTTPS over HTTP for canonical URLs
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, avoid the following practices:
- Avoid bad TLS/SSL certificates and HTTPS-to-HTTP redirects because they cause Google to prefer HTTP very strongly. Implementing HSTS cannot override this strong preference.
-
Don't include the HTTP version of your pages in your sitemap or
hreflang
annotations rather than the HTTPS version. -
Avoid implementing your SSL/TLS certificate for the wrong host-variant. For example,
example.com
serving the certificate forsubdomain.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.
Prefer URLs in hreflang
clusters
To help with sites' localization efforts, for canonicalization purposes Google prefers
URLs that are part of hreflang
clusters. For example, if
https://example.com/de-de/cats
and
https://example.com/de-ch/cats
reciprocally point to each other with
hreflang
annotations, but not to
https://example.com/de-at/cats
, the pages for
de-de
and de-ch
will be preferred as canonicals instead
of the /de-at/
page that doesn't appear in the
hreflang
cluster.
Read more about troubleshooting and fixing canonicalization issues.