What are canonical links?

Canonical links, also known as canonicals, are HTML attributes used in the head of a web page to tell search engines which URL is the primary source of a piece of content. They exist to avoid duplicate or near identical content across several pages and to make sure that search engines and visitors are shown the right page.

When should you use canonical links?

A common use case for canonical links is a page that exists in several URL variants, for example with or without www, or on different protocols (HTTP vs. HTTPS). A canonical link names the primary URL, so search engines do not treat the variants as duplicates and only one version gets crawled and shown in the search results.

Another use case is a page that is available on several domain names or subdomains. Here a canonical link states which domain or subdomain is the primary source of the content.

Canonical links can also be used when a page is available for several countries or regions and every region has its own URL. In that case a canonical link states which region is the primary target audience.

What role do canonical links play in online shops?

In online shops, canonical links can play an important part in avoiding duplicate and near identical content and in making sure search engines show shoppers the right product page. Filters and sorting inside a category, for example, can produce several URL variants of one product page. A canonical link states which of them is the primary source of the content.

Canonical links are just as useful when one product is reachable through several category pages or landing pages.

Do canonical links affect SEO?

It is worth keeping in mind that canonical links have no direct effect on your rankings in a search engine, but they do help you avoid trouble with duplicate content and near identical content.

In short: canonical links are HTML attributes in the head of a web page that tell search engines which URL is the primary source of a piece of content. They are used to avoid duplicate or near identical content across several pages and to make sure search engines and visitors land on the right page. Canonical links have no direct effect on rankings, but they do improve usability and the relevance of your content.

Want to know whether the canonicals on your own site point where they should? An SEO audit checks it page by page. taismo also runs a canonical tag generator, currently available in German only. More terms from this field are in the SEO glossary.