What is a Canonical Tag?
A canonical tag, or rel="canonical", is a snippet of HTML code that declares the canonical URL of a web page. It lets you define the main version of your duplicate, near-duplicate, and similar content under different URLs, instructing search engines on which version should be indexed.
Example of a Canonical Tag
Here's what a canonical tag looks like in the page code:
<link rel="canonical" href="/blog/">
An alternative to canonical tags is implementing a rel="canonical" HTTP header.
Why are Canonical Tags Important?
Using the canonical tag is the primary way to solve duplicate content issues on a website. A canonical tag helps search engines identify the most representative “canonical” version among duplicate pages to indicate what needs to be indexed and re-crawled more frequently. The tag also helps consolidate link signals from a set of duplicate pages to the canonical version (or the one you want to be ranked), thereby improving its overall ranking.
If you don’t use canonical tags on the duplicate pages of your site, Google will still attempt to identify the canonical page. However, there’s no guarantee that it will be the page version you want to be indexed.
Best Practices for Canonical Tags
1. Always Use the Self-Referential Canonical Tag
A self-referencing canonical tag references the URL of the given page, even if the page has no alternative versions. This practice is recommended because it clarifies which page you want to have indexed, consolidating all variations of the URL (e.g., with parameters, upper/lower case, www, and non-www).
2. Use Absolute URLs
Absolute URLs contain all the information necessary to locate a resource and help avoid unintentional mistakes or misinterpretations of canonical URLs by search engines. Although relative URLs can be used, it is best SEO practice to use absolute URLs in canonical tags.
3. Don’t Use the Robots.txt File for Canonicalization
The robots.txt file tells search engine crawlers where they can and can’t go on your site. If URLs are disallowed in robots.txt, Google won’t read their canonical tags, and link signals from these pages will not be consolidated.
4. Audit Your Website Regularly
Regularly monitor duplicate content issues on your website to ensure proper canonicalization of your pages. Tools like Ranktracker's Site Audit can help you find duplicate and near-duplicate pages that aren’t properly canonicalized.
FAQs
Is the Canonical Tag Always Necessary?
Although it is not strictly necessary to use the canonical tag, it is recommended. If there’s duplicate content without the canonical tag, Google may still try to find the canonical version. However, in the presence of a canonical tag, it becomes clearer to the search engine.
What is a Canonical URL?
A canonical URL is the URL of the preferred version of a page in a set of duplicate or near-duplicate pages. This URL is used in the canonical tag to instruct search engines about canonicalization.
For more insights on managing duplicate content and improving your website’s SEO, visit the Ranktracker Blog and explore our comprehensive SEO Guide. Additionally, familiarize yourself with key SEO terms and concepts in our SEO Glossary.
