rel=canonical: the ultimate guide to canonical URLs

rel=canonical: the ultimate guide to canonical URLs • Yoast

Joost de Valk

Joost de Valk is the founder and Chief Product Officer of Yoast. He’s a digital marketer, developer and an Open Source fanatic.

A canonical URL lets you tell search engines that certain similar URLs are actually the same. Because sometimes you have products or content that can be found on multiple URLs — or even multiple websites. By using canonical URLs (HTML link tags with the attribute rel=canonical) you can have these on your site without harming your rankings. In this ultimate guide, I’ll discuss what canonical URLs are, when to use them, and how to prevent or fix a few common mistakes!

Table of contents

The rel=canonical element, often called the “canonical link”, is an HTML element that helps webmasters prevent duplicate content issues. It does so by specifying the “canonical URL”, the “preferred” version of a web page – the original source, even. And this improves your site’s SEO.

The idea is simple. If you have several versions of the same content, you pick one “canonical” version and point the search engines at it. This solves the duplicate content problem where search engines don’t know which version to show in their results.

The SEO benefit of rel=canonical

Choosing a proper canonical URL for every set of similar URLs improves the SEO of your site. This is because the search engine knows which version is canonical, and can count all the links pointing at the different versions as links to the canonical version. In concept, setting a canonical is similar to a 301 redirect, only without the actual redirecting.

The history of rel=canonical

The canonical link element was introduced by Google, Bing, and Yahoo! in February 2009. If you’re interested in its history, I would recommend Matt Cutts’ post from 2009. This post gives you some background and links to different interesting articles. Or watch the video of Matt introducing the canonical link element. Because, although the idea is simple, the specifics of how to use it are often a bit more complex.

The process of canonicalization

Ironic side note

The term Canonical comes from the Roman Catholic tradition, where a list of sacred books was created and accepted as genuine and named the canonical Gospels of the New Testament. The irony is it took the Roman Catholic church about 300 years and numerous fights to come up with the canonical list, and they eventually chose four versions of the same story…

When you have several choices for a product’s URL, canonicalization is the process of picking one of them. Luckily, it will be obvious in many cases: one URL will be a better choice than others. But in some cases, it might not be as obvious. This is nothing to worry about. Even then it’s still pretty simple: just pick one! Not canonicalizing your URLs is always worse

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This article was written by Joost de Valk and originally published on SEO blog • Yoast.

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