Subdomain

A subdomain is a prefix such as blog.domain.com. It separates areas such as language, shop or login technically and organisationally. For SEO, it is often treated as a separate website; content meant to strengthen the main domain usually belongs in a subdirectory.

A subdomain is a prefix that divides a domain into separate areas. It is placed in front of the actual domain and separated by a dot – for example shop.example.com or blog.example.com.

In the Domain Name System (DNS), internet addresses follow a fixed hierarchy that is read from right to left. On the far right is the top-level domain (e.g. “.com”), before it the second-level domain, i.e. the actual name (e.g. “example”). Everything in front of it is a subdomain at the third or a lower level – which is why it is also called a third-level domain. Strictly speaking, “www” is also a subdomain. Technically, each subdomain can point to its own server or application.

What are subdomains used for?

Subdomains are suitable for separating areas of a website technically or organisationally. Typical uses are:

Language or country versions
A shop or blog on its own system
Campaigns and landing pages
Technical services

A well-known example is de.wikipedia.org: the “de” stands for the German-language version and is a subdomain. Subdomains can therefore separate different language versions. For country versions, however, subdirectories (example.com/de/) or separate country domains (.de, .ch) are also possible; which variant fits depends on technology, organisation and target markets. What's not advisable: creating a separate subdomain with similar content for each city – that creates many weak, interchangeable pages.

A subdomain can make sense if an area runs on a different system from the main website – such as a shop, a blog on its own CMS or a help centre. Large providers do this too: Google, for example, runs services such as maps.google.com or support.google.com as subdomains.

One advantage: subdomains can be short and memorable, such as help.example.com instead of a long directory address. They can also be operated technically independently, for example on a different server.

Campaign and landing pages are sometimes also run on subdomains, for example when they're created with a separate page builder. For SEO, however, this is usually not ideal (see below).

Technical services are also often integrated via subdomains – for example a password-protected customer, dealer or employee area under login.example.com, a staging environment under staging.example.com or a mail server.

Subdomain or subdirectory?

Subdomains and subdirectories are often confused. A subdomain comes before the domain (blog.example.com), a subdirectory after it (example.com/blog/). Subdomains are set up in DNS or with the hosting provider and can point to their own server; subdirectories are part of the same website and are created in the shop system or CMS.

Importance of subdomains for SEO

In principle, Google can crawl and rank content on subdomains and in subdirectories equally well. In practice, however, subdomains are often treated more like separate websites: the strength of the main domain – for example from backlinks – doesn't benefit them to the same extent as a subdirectory. For content that is meant to strengthen the main website, such as a shop's guide or blog section, subdirectories are therefore usually the better choice. Subdomains are suitable when an area is to be clearly separated technically or in terms of content. Important: each subdomain needs its own robots.txt and should be covered in Google Search Console, ideally via a domain property that includes all subdomains.