A subdomain is an extension to the main domain of a website and can be useful for implementing multinational or multilingual versions of a site. Search engines treat subdomains as independent from the main domain, so it is important to understand best practices for optimisation. Our Hangout Notes cover these best practices, together with real world examples and advice from Google.

External Link Signals Are Only Passed Between Domains & Subdomains via Internal Linking

May 29, 2018 Source

Signals from your external links can be passed via internal linking between a domain and its subdomains. These signals aren’t shared automatically to the main domain if someone links to your sub-domain, for example.

Redirect Old URLs When Migrating Images to a New CDN

May 18, 2018 Source

When migrating images to a new CDN, make sure to redirect the old image URLs to the new ones as well as updating the embedded links in the webpage. Images aren’t crawled as frequently as webpages so you need to make sure all signals are aligned so Google can move them over as quickly as possible. Consider setting up a subdomain and transferring the images, so the URL doesn’t change except from the hosting.

Microsites Can Be Seen as Doorway Pages

November 3, 2017 Source

Microsites often look like a collection of doorway pages. If you are looking to build these microsites up in the long run then this might be an option, but if they don’t have value beyond driving traffic to another site, then microsites aren’t recommended for search and should be noindexed.

WWW Subdomain Should Not be "Parked"

August 12, 2016 Source

If the www version of your domain is "parked", it might affect the indexing of the other versions of your domain.

Subdomains for multiple sites

February 26, 2016 Source

Subdomains are treated as separate sites, or part of the main domain depending on the signals.

Google Recognises Separate Sites on Subdomains

February 23, 2016 Source

Google has a process to recognise when separate sites are hosted on subdomains, and when they are used for a single website. They will then apply per site e,g, penalties and malware detection, but this can affect the entire domain if they haven’t recognised them as different sites.

Wildcard Subdomain Configuration Causes Crawl Issues

December 23, 2014 Source

Using wildcard subdomains can make a site difficult to crawl.

Sub-Domains May Be Treated as a Separate Site

October 6, 2014 Source

Sometimes sub-domains are treated as independent websites, depending if Google can detect they are related or not. So a closely linked blog on a sub-domain is going to be OK.

Only Manual Penalties Show in Search Console

September 26, 2014 Source

Only manual Google penalties are shown in Webmaster Tools. They can be applied to a single subdomain, or all subdomains of a domain. They are removed automatically after a fixed period.

Related Topics

HTTPS Parameters Site Architecture URL Architecture Canonical Domain Facets TLDs Site/Page Quality