The canonical tag is a tag written in the head part of the HTML page. Its function is to tell search engines which page is the original page, avoid duplicate content issues and concentrate page weights. It declares the content source in the form of , and is often used in the case where multiple parameter variant links point to the same main page in e-commerce websites. When using it, please note: ① It must be placed in the head area; ② It is recommended to use absolute addresses; ③ Support cross-domain use; ④ The content of the pointing page should be highly similar. Common errors include address errors, closed-loop canonical, conflicts with noindex, etc. Suitable usage scenarios include: pages with the same content and only different parameters, articles are published in multiple columns, and different URLs on mobile and desktop versions. Correct application can help search engines better understand website structure and reduce SEO risks.
The tag link rel="canonical"
is added, mainly telling search engines: although the content of this page may appear on multiple websites, which one should you recognize as the "authentic" original page. Simply put, it can help you avoid duplicate content issues and concentrate page weights.

What is a canonical tag?
is a tag written in the
section of the HTML page. Its purpose is to tell search engines: "Hey, even if this page looks similar to other pages, it's copied from that link, please count the weight to that original page."
This situation often occurs on e-commerce websites, such as a product page with multiple sorting or filtering parameters:

https://example.com/product?color=red https://example.com/product?color=blue https://example.com/product
At this time, you can add the canonical tag to https://example.com/product
to each variant page to let search engines know which page is the main page.
How to use canonical tags to be effective?
There are several key points to pay attention to when using:

- Write in the head : Make sure to be placed in the
<head>
area, otherwise it may not be recognized. - Absolute addresses are more secure : Although relative paths can also be used, it is recommended to use a complete URL to avoid confusion.
- Cross-domain can also be used : if you copy your own content (such as reprinting) under another domain name, you can also use canonical to prevent it from being treated as plagiarism.
- The content should be similar to the current page : don't point it randomly, canonical is not used to jump, but to declare the "content source".
For example:
<head> <link rel="canonical" href="https://example.com/original-page"> </head>
Common Errors and Precautions
Sometimes, if you use it, you will have problems because you have stepped on these pitfalls:
- ? Canonical is written as the wrong address : for example, a spelling error or pointing to a page that does not exist, which means that it is not written.
- ? Multiple pages canonicalize each other to form a closed loop : A points to B, B points to C, and C points back to A, and the search engine will be confused.
- ?Using noindex and adding canonical : noindex means not to be included, but canonical wants to pass weights, which has a logical conflict.
- ?Dynamic pages automatically generate canonical : For example, CMS such as WordPress or Shopify can generally be processed automatically, but you need to confirm whether the output is correct.
When should I use canonical?
- The page content is basically the same, but the parameters are different (such as sorting and tracking code)
- The same article is published in multiple columns or sub-sites
- Mobile and desktop versions use different URLs (responsive designs are more common now, but old systems may still exist)
In this case, adding the correct canonical can help search engines better understand your website structure and reduce the SEO risks brought by duplicate content.
Basically, that's not complicated to use, but it's easy to ignore details. As long as you don’t point out randomly or conflict, you can play its due role.
The above is the detailed content of Using `link rel='canonical'` in HTML. For more information, please follow other related articles on the PHP Chinese website!

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