What is a preferred domain and how does the domain tool work?
- The Google Preferred Domain Tool
Search engines may get increasingly savvy, but domains can still run into trouble with their canonical domain (i.e http://example.com vs. http://www.example.com). And what precisely is 'your preferred domain'? Well, you might say that you have only one domain for your site, that there is no preference or preferred domain to choose! However consider the two example.com URLs above. The structure of these sample URLs will nearly always point to the same location on a server. However, search engines can not make that assumption - they could, for example, refer to different content intended to sit on the different subdomains. For this reason it is not possible for search engines assume that it's OK to roll the two together.
This creates a problem for search engines with duplicate content, and extends into considerations for links to the site, traffic, page rank, algorithms, supplemental results and so on. This is why the preferred domain for a site it is still a major issue to be aware of.
Have you set your preferred domain and is this an issue for you currently?
To check if your site has pages listed with both 'www' and 'non-www' listings perform the google search [site:example.com -inurl:www], and inspect the results for non-www listings of some or all of your pages. If your site has this issue appearing as two different listings in our search results, you essentially have duplicate content. Not the worst kind of duplicate content, but still a definite issue that can become convoluted with other issues and cause you problems in Google and other search engines. For example, Google will often hold supplemental results where the result is for duplicate content of whatever Google considers to be the "main" site. This can include 'www' versus 'non-www' content. This is another important factor, and you should indicate your preferred domain; your lead domain for the site.
The Google Preferred Domain Tool
The easiest way to so indicate your preferred domain is to set the preferred domain using the Google Webmaster Tools section for a site under the Google Sitemap or Google Webmaster Console. You'll need a log-in, and to verify your site under your own log-in. Also, you might have 301 redirects in place already, in which case you may feel you don't have to use the Preferred Domain Tool. Google can follow these redirects. However, if you use the Preferred Domain Tool, you can still benefit - Google say they will be able to more easily consolidate links to your site and, with time, Google will specifically direct the Googlebot to the preferred URL versions of your site's content.
Once I've set my preferred domain, how long will it take before I see changes?
Google has indicated that the time taken for changes to filter through varies around a number of points. These include your sites crawl frequency, and how many pages are indexed with the non-preferred version. After a few weeks have passed since adjusting your preferred domain, you should see the change in the SERPs.
