The canonical tag is used to correctly mark websites with duplicate content. This will be punished as soon as it is recognized by Google. That is, the page with the repetitive content ranks poorly in the search results. In the header area of the source text, it is identified within a link element with the rel = “canonical” attribute. This is how you link one or more copies of a website to the original. This original page is also referred to as the “canonical” page.
If a crawler scans a website and finds a canonical tag on it, the bot recognizes that the linked page is the “real” original, so the “copied” websites can be ignored with regard to duplicate content. In addition, the search engine such as Google transfers properties such as PageRank to the original. Thus, the Canoncial Tag is an important tool for OnPage optimization and for avoiding errors in the evaluation of content.
When is the Canonical Tag used?
Online shops, whose products can be sorted once by color and once by price, get a lot of duplicate content as a result. Blogs that want to display the same content more often, for example if an article about chocolate desserts should appear under the “Desserts” and “Chocolate” categories, also have duplicate content. This is problematic because if there is no canonical tag, the indexing of the content is arbitrary or the content can be devalued. A canonical tag can also be used if the content of a page is offered under a further URL, for example as a print version or PDF, as is often the case with press releases.
In addition, a canonical tag is helpful for so-called “technical duplicate content”, i.e. when the page can be reached with and without www or https. This is especially true for standard urls such as “index.html” and “home.html”, which refer to the same content.
According to definitionexplorer, the use of canonical tags is also recommended when creating independent mobile websites (for example: m.Bebeispielseite.de) with their own URL, so that the advantage of mobile optimization does not become a disadvantage.
The Canonical Tag gives the search engine crawlers a clear indication of which content is to be assessed as the more relevant and avoids errors when the algorithms rate the page.
How is the Canoncial Tag used?
There are two options for using canonical tags:
On the one hand, you use the source code of the content page, which is a copy of a page (e.g. ” www.beispiel.de/kopie-der-original-url “) and insert the following code in the header or in the HTTP header:
<link rel = ”canonical” href = ”http://www.beispiel.de/original-url” />
Using the example on this page, it looks like this:
Only one canonical can be read per URL. If there are several canonical tags in the source text, these will be ignored by the search engines and the page will still be indexed.
It is important to ensure that no meta tags such as “nofollow”, “disallow” or “noindex” have been assigned within this source code, as these can interfere with their functionality with the canonical tag. It is important to pay attention to which of the URLs are marked with the canonical tag, as these are used by search engines such as Google not be listed.
The second variant is to pass the canonical property via the server. If, for example, a shopping cart page is generated in an online shop, the server also sends the information that it will receive a “canonical tag” for the original page. This prevents automatically generated pages from creating duplicated content.
This is also useful if visitors to the website can filter content using IDs. For example, only look at “green” items in online shops. On the page created by the system, the content would be the same as the original page – although this is displayed on a new URL. In this case, too, it is advisable to pass the canonical property within the link attribute for the original page within the source text.
What should you watch out for when using the canonical tag?
- Before using the canonical tag, it is essential to check whether there is really duplicate content.
The content of the pages should actually be identical or largely the same.
There are various duplicate content checkers available online that do this.
For example, if there are articles in a blog in several languages, the search engines will not evaluate them as the same content, even if the statements made in the text match.
Video statement by Matt Cutts / Google
- The URL identified by the canonical tag must be reachable and must not refer to a 404 page. This happens, for example, if a “www.” Is forgotten or the website being accessed has a changed url.
- The URL must have the exact name; an additional or missing slash or “/index.php” at the end can cause an incorrect canonical tag.
- Only one canonical tag may be used per website, otherwise search engines like Google will ignore this distinction.
- Absolute URLs (with http: //) should always be linked. The canonical tag also accepts relative URLs (example.de/artikel), but the linked page is then linked to http://example.de/beispiel.de/artikel.
- The linked page and the url with canonical tag must not have a “noindex”, “ nofollow ” or “disallow” meta tag.
- Pages with a canonical link are not included in the search results – with the exception of the pages that refer to themselves with a canonical link in order to prevent possible URL generation via session IDs.
- The use of canonical tags does not make sense for paginated pages that are marked with rel = “next” or rel = “prev” (since there is no actual duplicate content at this point).