How to Specify a Canonical with rel="canonical" and Other Methods | Google Search Central  |  Documentation  |  Google for Developers (original) (raw)

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:

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:

Best practices

For all canonicalization methods, follow these best practices:

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 element in the code for all duplicate pages, pointing to the canonical page. Pros: Can map an infinite number of duplicate pages. Cons: Can be complex to maintain the mapping on larger sites, or sites where the URLs change often. Only works for HTML pages, not for files such as PDF. In such cases, you can use the rel="canonical" HTTP header.
rel="canonical" HTTP header Send a rel="canonical" header in your page response. Pros: Doesn't increase page size. Can map an infinite number of duplicate pages. Cons: Can be complex to maintain the mapping on larger sites, or sites where the URLs change often.
Sitemap Specify your canonical pages in a sitemap. Pros: Easy to do and maintain, especially on large sites. Cons: Google must still determine the associated duplicate for any canonicals that you declare in the sitemap. Less powerful signal to Google than the rel="canonical" mapping technique.
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.

Google supports explicit rel canonical link annotations as described inRFC 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).

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:

  1. Add a <link> element with the attributerel="canonical" to the <head> section of duplicate pages, pointing to the canonical page. For example: Explore the world of dresses ****
  2. If the canonical page has a mobile variant on a separate URL, add arel="alternate" link element to it, pointing to the mobile version of the page: Explore the world of dresses ****
  3. Add anyhreflang 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/green-dress.html

Bad example:/dresses/green/green-dress.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 section is valid HTML.

If you use JavaScript to add the rel="canonical" link element, make sure toinject the canonical link element properly.

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 byRFC5988 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.

Use a sitemap

Pick a canonical URL for each of your pages and submit them in asitemap. 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. Allredirection 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:

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 inhreflang 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:

Although our systems prefer HTTPS pages over HTTP pages by default, you can ensure this behavior by taking any of the following actions:

To prevent Google from incorrectly making the HTTP page canonical, avoid the following practices:

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, ifhttps://example.com/de-de/cats andhttps://example.com/de-ch/cats reciprocally point to each other withhreflang annotations, but not tohttps://example.com/de-at/cats, the pages forde-de and de-ch will be preferred as canonicals instead of the /de-at/ page that doesn't appear in thehreflang cluster.

Read more abouttroubleshooting and fixing canonicalization issues.