Canonical URL
What is Canonical URL?
In the SEO industry, a canonical URL is crucial for managing duplicate content issues. When multiple pages have similar or identical content, search engines may get confused about which page to rank. By using a canonical tag, you can signal to search engines which URL you consider the 'master' version. This helps consolidate link equity and avoids potential penalties for duplicate content. For instance, a webpage can be accessible through different URLs like with or without 'www', or with different parameters. A canonical URL tells search engines to treat these variations as a single entity, thereby focusing all ranking signals on one preferred URL. Implementing canonical URLs correctly can significantly impact your website’s SEO performance by ensuring that the most relevant page is ranked, and that all the link juice flows to that preferred page.
A canonical URL is the preferred version of a web page that search engines should index and rank.
Examples
A website's homepage may be accessible via 'http://example.com' and 'http://www.example.com'. Setting 'http://www.example.com' as the canonical URL ensures that search engines treat both URLs as one and the same, preventing dilution of ranking signals.
An e-commerce site might have product pages that can be accessed with different query parameters, such as 'http://store.com/product?color=red' and 'http://store.com/product?size=large'. By setting 'http://store.com/product' as the canonical URL, the site ensures all variations are considered as one page by search engines.
Additional Information
Canonical tags are added in the HTML code's <head> section as <link rel='canonical' href='preferred-URL'>.
If not set manually, search engines might automatically choose a canonical URL, which may not always be the preferred one.
References
Canonical URLs: A Beginner's Guide to Canonical Tags - Semrush
What is a Canonical URL? A Guide for SEO - Search Engine Journal
What is a Canonical URL? Best Practices for SEO - Ahrefs