Canonicalization, sometimes referred to as standardization or normalization, is a computer science process that converts data possessing more than one possible presentation into a standardized, normalized, or canonical form. If we had to rephrase that definition in simple terms, it is a method for combining data that has the same content but different labels under one common name. When it comes to Search Engine Optimization (SEO), canonicalization is the process of ensuring the Uniform Resource Locators (URLs) that refer to your website’s location on the Internet, conform to one single universal address.
The Rise of URL Variations
In the early days of the World Wide Web, the standard URL for any website started with a ‘www’ prefix appended to the beginning of a domain name. If you wanted to navigate to a specific site, you would need to type www.cdnsun.com in your browser’s URL address bar. However, as time moved on and the Internet matured, many sites opted to drop the ‘www’ prefix. So instead of typing www.cdnsun.com, you now only needed to enter cdnsun.com to go to the same website. This evolution in using the naked domain instead of a subdomain prefix resulted in multiple URL variations that all reference the same Internet location.
Elaborating on the example above, if you enter www.cdnsun.com or cdnsun.com into your browser’s URL bar, you will reach the same website. Other websites may leverage even more URL variations such as example.com/index.html and exmaple.com/home.html. Although the use of these various URLs has grown in popularity over the years, making it easier for end-users to find a specific site or online service, it can damage a site’s Search Engine Optimization.
Poor Canonicalization Negatively Affects Your SEO
Search engines use crawlers to index content for their search results. The problem with multiple URL variations for the same website is that the web crawlers see each URL as a separate site or service. The crawler bot will effectively index the website for each URL variation resulting in the votes split by the number of unique URLs. Extrapolating this example further, as search bots will crawl the website for each URL independently, every resource, whether it be a page, image, video, or the content itself is indexed multiple times and referenced by the search engine using each unique URL. As these crawled links all refer to the same site and content, the result is a diminished SEO score. In the online marketing world, original content is king. Creating an effective SEO strategy starts with creating content or online services that people need. Implementing an effective canonical URL scheme is only a component of an efficient SEO plan. You still need to generate the differentiating pull to get visitors to your site. However, good content and efficient canonicalization is a far better option that good content with multiple URL variations for the same website or service.
Setting Your Canonical URL
There are several methods you can use to configure a canonical URL for your website. However, before you implement one of the documented approaches, you must identify your preferred URL and ensure it is the only one linked to your SEO strategy. Once you have selected your canonical URL using the Google Search Console, you could either add an HTML link tag in your code, configure an HTTP 301 redirect, or leverage a canonical HTTP header.
Use the Google Search Console for Canonicalization
As Google controls a consistent share of over 85% of the search engine market, it is prudent to leverage its toolset when you need to identify and set your canonical URL. The Google URL Inspection Tool provides you with the ability to see the current index status, inspect a live instance, and request indexing for a particular URL. Leveraging this tool will help you identify your site’s canonical URL, as seen by the largest search engine on the Internet. The only disadvantage is that it will only show you what Google sees. However, due to its leading position in the search engine market, this perceived disadvantage can be safely ignored.
Adding an HTML Link Tag to Your Code
If you have identical pages created by multiple URL variations, you can add the rel=”canonical” link tag to the <head> section of your HTML Document Object Model (DOM). For example, if you have two explicit URLs, such as example.com and www.example.com, and settle on example.com being your canonical URL, in the <head> section of your www.example.com page you would insert the following link tag: <link rel=”canonical” href=”https://example.com”. The advantage of using this method is that it can map an infinite number of duplicate pages. However, it does have its disadvantages. Using the rel=”canonical” link can add to the size of the page impacting its performance. It can also be a challenge to maintain, especially if you have a large site or host a service where URLs change often. The other drawback is that this technique only works with HTML pages and not for document objects such as PDF files.
Leveraging Your HTTP Header
If you have access to the webserver hosting your site, you can configure it to use the rel=”canonical” HTTP Header. This configuration sets the canonical URL for non-HTML objects such as PDF files or other downloadable artifacts. HTTP headers are remarkably useful configuration tools you can use for everything from cache-control settings to securing your origin server. The advantage of using this approach is that it does not increase your page size, and like the HTML link tag, it can also map an infinite number of pages. It also shares the disadvantages of being difficult to maintain in larger sites or services where URLs change regularly.
Use a Sitemap
Using a sitemap gives you the ability to provide a search bot with information about pages, images, videos, and other files on your website. It also indicates the relationship between the different objects. When a web crawler such as the Googlebot encounters a sitemap, it leverages the information in the document to crawl the site intelligently. The advantage of using this approach is that it is easy to maintain for larger websites. However, it does have its drawbacks. The web crawler must determine the associated duplicate URLs you declare in a sitemap, and it is not as powerful as the explicitly stated rel=canonical technique.
HTTP 301 Redirect
An HTTP 301 redirect tells a bot or browser that a particular URL has moved permanently. If you have access to the server that hosts your site, you can configure a redirect using the built-in capabilities of the specific webserver, be it Apache, IIS, or NGINX. Using this method aids the web crawler in identifying and indexing the correct canonical page. If you manage a site where you have duplicate pages, you can also use this method to implement canonicalization. However, you must bear in mind that this technique is a permanent redirect and its use limited to identical pages on the same site, or if the page itself is obsolete.
Canonicalization and SEO
As the world continues to embrace eCommerce and other digital services, the roles of search engines in Internet marketing is now more vital than ever. Typically, the first thing an individual or business does when looking for a particular product or service is to conduct a web search. If your site or business competes in today’s digitally-driven economy, people need to find your site or service with ease and efficiency. Search Engine Optimization is the science that provides the tools and techniques you need to ensure your site ranks as high as possible on any search index. Although canonicalization is not an SEO silver bullet, it remains an indispensable component you need to leverage in any Search Engine Optimization strategy.