Canonical URL
A canonical URL is a tag that tells search engines which address is the main one when the same content can be reached from several addresses. It is written in the page code as rel="canonical". Duplicate addresses then stop splitting each other's strength.
What is a canonical URL?
A canonical URL is the main address of a piece of content. It is set in the page code with a rel="canonical" tag. When the same content appears at several addresses, it tells search engines which one is the real one.
Here is an everyday case. A product in your online store opens at both /shoes/white-trainers and /sale/white-trainers. Visitors from ads also arrive with extras such as ?utm_source=... on the end. To a person these are all one page. To a search engine they are separate addresses. The canonical tag makes them all point to the first address, and that address shows in search results.
Why does it matter?
Duplicate addresses make it harder for a search engine to decide which page to show, and the value of incoming links can get split between them. The canonical tag pulls that together. It works as a hint, and a search engine may decide differently if other signals disagree. That is why internal links, the sitemap and the canonical tag should all point to the same address. If a page has moved for good, use a 301 redirect instead.
The canonical tag is one of the technical parts of SEO. We explain how to keep addresses intact in redesign without losing SEO. On the sites we build, every page writes its canonical address automatically, as described on our web design page.
Frequently asked questions
What is the difference between a canonical tag and a 301 redirect?
A 301 redirect sends visitors from the old address to the new one, and the old one no longer opens. With a canonical tag both addresses open, but search engines are told which one is the main one.
Should every page have a canonical tag?
Yes, it is a good habit. A page with no duplicates points to itself. That way, addresses with added parameters later cause no trouble.
How can I see which canonical Google chose?
The URL Inspection tool in Google Search Console shows which address Google picked as canonical.
Sources
- 01 How to specify a canonical URL with rel="canonical" and other methods · Google Search Central