Canonical URLs first appeared in 2009. This method, also known as a canonical link or canonical tag, is used in the world of SEO (search engine optimization) to avoid duplicate content. In the words of Google, a canonical URL is the URL of the page that Google considers most representative of a set of duplicate pages on a website.
Canonical tag syntax is placed in the <head> section of a website's source code and leads to canonical URLs that have or display the same or very similar content. This address is read by web search engine algorithms as a warning that this is the page to which users should be </head>redirected when searching these sites.
Its use is quite simple: the references "rel" and "href" are used. For example, if the preferred URL is "sitedirection / home", then a <link> element is added to the header section of the page:
<link rel="“canonical”" href="“sitedirection/home”/">.
Another way is to insert it into the HTTP header, in cases where there are speed problems:
<https: sitedirection="" home="">;rel=”canonical”</https:>
It is of vital importance to use tags and create canonical URLs when there are several pages with the same content, or very similar within a website. Either totally or in part, but you want to give more importance to the web positioning of a page above others.
Website administrators can create different URLs with the same content, for different reasons:
Duplicate content scenario in e-commerce: an electronic store may have different URLs for the home page or different pages for variations of the same product; depending on the specific color, model or size, another for the mobile version of the page, or for different regions or languages. For all these pages it is important to use canonical tags, if you want to be at the top of the search results.
Making canonicalization errors is very common, so the website should be checked frequently to address such problems. Some of these errors captured by the auditing tools are:
- Canonical points to 4XX, it is activated if one or more pages are canonicalized to a 4XX URL, since search engines do not index 4XX pages because they do not work. Therefore, any canonical tag pointing to such pages is ignored and the incorrect (non-canonical) version of the tag is indexed. To correct this, you must review the affected pages and change the dead canonical links (4XX) for links to pages with functions (200) that you want to index.
- Canonical points to 5XX, it is activated if one or more pages are canonicalized to a 5XX URL, because the HTTP 5XX status codes warn that there are server problems resulting in a canonical page that cannot be accessed. To resolve this, simply replace any erroneous canonical URLs with valid ones. Then check the server for misconfigurations if the specified canonical appears to be correct.
- Canonical points to redirection, it is activated if one or more pages are canonicalized to a redirected URL, because canonicals must point to the most authoritative version of a page. This is not the case with URL redirection. Therefore, search engines may misinterpret or ignore it. To fix this, the canonical links must be changed to direct links to the higher authority version of the page.
- Duplicate pages without canonical, this warning appears if there are one or more duplicate or very similar pages that do not indicate a canonical version because the search engine will try to identify the most appropriate version to show in the search results; it is possible that this is not the version that is intended to be indexed. This is solved by reviewing the groups of duplicates, choosing a canonical version to be indexed in the search results and indicating this as the canonical version in all duplicates, and adding a self-referential canonical tag to the canonical version.
- Hreflang to non-canonical, is activated if one or more pages specify a non-canonical URL in their hreflang entries, since the links in the hreflang tags always have to point to the canonical pages. To solve this, you only have to replace the links in the hreflang entries of the pages affected by your canonical.
- Canonical URL has no internal inbound links, it is activated if one or more indicated canonical URLs have no internal inbound links, because the orphaned canonical URLs are inaccessible to website visitors. To fix this, any internal links to canonical pages must be replaced with direct links to the canonical
- Non-canonical page in sitemap, is activated if one or more non-canonical pages are shown in the sitemap, since search engines assume that non-canonical URLs should not be included in the sitemap. To fix this, the non-canonical URLs must be removed from the sitemap.
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