Stasia Avet
Mar 19, 2019 | 9 min read

Let’s say you have a website and want to separate a massive piece of content by putting it into a subdomain. Or maybe you’ve got a website with subdomains that you need to promote. In both cases, you’ve got to know what to do with your site SEO-wise because subdomain optimization is tricky.

In the next paragraphs, we’ll explain what subdomains are, why you might need them and how to promote them in a search.

What is a subdomain?

A subdomain is a subset of your website, serving to organize or divide your website content into distinct sections.

But how is it related to the domain?

A long, long time ago, back in the days of the ARPANET, domain names, as we know them today, did not exist. Instead, all directories in the network were marked with code numbers – IP addresses. That’s what you would’ve had to use in the 1970s to get to Instagram –, or Facebook –

But in 1983, Paul Mockapetris invented the DNS concept – Domain Name System – that we are all still using to this day.

The main idea of DNS lies in its tree-like hierarchical structure: from the main domain to the subdomains.

The main domain is called the Top-Level Domain (TLD). Your unique website’s name would be the Second-Level Domain (SLD). A subdomain, in turn, is a third-level domain.

Take a look:


Regarding top-level domains – there are lots of them: .net, .org, .edu, .gov and regional ones: .it, .ru, .es, etc. Second-level domain is what makes your website’s address unique. And subdomains can have it any custom name: blog., help., store., online., etc.

If you already have a registered domain, you can create a subdomain for free, but you have to update your registration with the info that you’re creating a 3rd-level domain.

Let’s figure out when you’d need one.

Subdomain use cases

You need a subdomain if you have several types of content under the same domain, and, as a result, your users are puzzled and confused or the content pieces start getting in each other’s way in search results.

For example.

1. When you want to separate content by region

As a franchise business with offices in different countries or cities, you want to promote certain items or services in a specific area.

Subdomains will help you split local keywords and links for different regions so they don’t overlap and compete with each other.

It also can be useful for an informational website. For example, has subdomains for each city it publishes ads for:Craigslist city subdomains Or Wikipedia that shows content for each country on a specific subdomain:

Wikipedia's subdomains for regions

Google prefers websites having ccTLD – Country-Code Top-Level Domains – with each regional version being put on a separate domain:

Amazon's domains for different countries

But in order to do this, you need to buy each domain separately which can be quite expensive.

Before deciding on regional subdomains or country domains, you should consider all the pros and cons: what is easier to implement, what is less time-consuming to maintain, etc.

2. When you want to distinguish content based on its purpose

Some websites include various kind of information: product catalogue, blog, forum, knowledge base, members area for registered users, etc.

All these pieces of content may contain different information and can include varying functionalities and databases. In this case, subdomains are used to separate them from one another.

Look at the subdomains of WooCommerce – a customizable e-commerce platform for small and medium business:

WooCommerce themes subdomain – examples and demos of the e-commerce site themes.
WooCommerce documentation subdomain – guides, manuals, documentation, and tutorials for Woo’s products.
WooCommerce forum subdomain – forums.

You see that these subdomains have different both interface and purpose.

In the same way, you may need to segregate your help section (, store (, blog (, cloud service (, etc.

Take a look at this list of the most popular subdomains to get an idea of why people create subdomains.

3. When you need to split product categories

It’s especially common for e-commerce websites or retailers to offer multiple categories of items for sale. For example, giant Chinese retailer AliExpress has several subdomain-levels, both for country and item categories:

AliExpress regional and category subdomains

The thing is that it’s easier to run a large website when it’s split into subdomains. Thus, subdomains can be managed by different people, with each team being responsible for a separate item category or region.

4. When you want to categorize a huge volume of content

Having subdomains for different product groups on e-commerce websites is similar to having 3rd-level domains for multiple content blocks on big media platforms.

For example, BuzzFeed has its main www subdomain, but also:

BuzzFeed's subdomains
As you can see, these content units are basically different projects under BuzzFeed’s umbrella. They target a different audience and have different purposes as well. And they definitely require separate managers who’ll be responsible for each of these subdivisions.

Tracking data on each one of them is much easier when they are split into subdomains.

5. When you have a mobile version of the website or an app

The mobile version of a website is basically a different website: it attracts different traffic using different acquisition channels. So one of the ways to satisfy the needs of mobile users and track all the needed data is to create an “m.” subdomain. Like,, and many others. Keep in mind though that Google recommends using responsive design because it’s easier for developers to implement and maintain it, and doesn’t create extra difficulties for search engines.

You’ll also need a subdomain for brand apps, e.g. or app.sendgrid.comAnd for web versions of apps:,, etc.

6. When you want to test new things on your website

One of the best things about subdomains is that you can use them for testing a new design or new CMS.

Testing a new CMS won’t influence the work of the main domain in any way. You can launch a new engine for your subdomain, test all of its features and learn how applicable it is to your website’s functionality. You can also tune the CMS to the special requirements of your hosting service. And only after having all tests done to your utter satisfaction you can move it to the main domain or to the entire website. During such tests, your website functions with no interruptions, generating traffic and revenue.

Test subdomains are usually secured by a password, so neither search engines nor users can access it. It’s also closed for the bots of the services that run website audits, which means you can’t use most automated audits to scan test subdomains.

In SE Ranking, though, you can give the bot permission to scan your closed domains. If you want to be sure everything works fine on your testing domain before you show it to the search engine, you can use our Website Audit.

To give the parser access to your test domains, enter your login and password into the parser settings:How to audit test subdomain

That way, you’ll catch things that might go wrong before Google spots any malfunctions.
Evidently, there are lots of cases when subdomains are the best way out. Now let’s sort out how search engines treat them, how subdomains affect rankings of the main domain and how to optimize them for better results.

Must-remember things about SEO for subdomains

Your subdomains and your domain are different websites.

It defines the whole SEO strategy for subdomains. Let’s sort it out step by step.

Webmaster settings for subdomains 

Уou need to register each one of your subdomains in webmaster panels separately. Here are Google’s instructions on how to submit website properties to the Search Console:

Google Analytics will track the entire website, but you can set goals, filters, and get reports for your subdomains in particular. Read here: how to get data on your subdomain traffic.

Content strategy 

Identical texts on the domain and subdomain are duplicate content. No point in creating a subdomain if you don’t have enough unique content or if it doesn’t differ much from the one you have on the main domain.

To reduce common content duplicates (e.g. landing page presenting a product for different regions), use rel=”canonical” to show the prioritizing page. After creating a good new page on your subdomain, don’t forget to interlink it with your domain. And make sure you add it to the website’s sitemap so it gets indexed quicker.


You’ll have to build a link profile from scratch. Backlinks of the main domain don’t spread authority to subdomains. Besides, sometimes subdomains differ dramatically from the main domain (independent project, specific product type, etc.) which is why backlinks should also come from thematically different sources.

Tech nuances

  • You’ll need different robots.txt files for each subdomain. Keep in mind that your www. robots.txt file won’t be valid for any other subdomain or the main domain.
  • You’ll need separate XML maps.
  • Add the hreflang attribute for subdomains in different languages.
  • To make Google index your subdomains faster, make sure you are interlinking your main domain and subdomains. But don’t expect the domain to help subdomains to rank higher. The SEO for them are separate projects and would need to start from scratch. 

Tracking SEO results for subdomains

You can track your subdomains together with your main domain or separately. For example, in SE Ranking Keyword Rank Tracker you can choose either option the following way:

Tracking subdomains together with the main domain. When creating the project, go to the Advanced options and put a checkmark in the “Match subdomains” checkbox.How to check rankings of subdomains Thus, the service will take into account the pages of all your subdomains when calculating your SERP rankings.

Tracking each subdomain separately. For this, you need to create a separate project for each subdomain you want to monitor:

How to track subdomains separately

Enter the subdomain address into the “Website URL” field. Thus, the service will only check rankings for the given subdomain and its subdomains (4th level and further), e.g.,,, etc.

Can subdomains harm your website’s SEO?

Google’s John Muller claims that the engine knows how closely subdomains and their domain are bounded. But technically they are different websites. Take the websites created as subdomains for It answers the question, whether a subdomain can harm your domain’s SEO. The answer is ‘no’ if you are playing fair.

However, if you have malware subdomains, Google can label the whole domain as malicious.

Also, If you try to push your subdomains/domain in search for the same queries, Google can penalize your domain.

The worst case scenario is when you find indexed subdomains (that you were unaware of) with duplicate content or the test ones – those are really harmful and they are hard to find.  

Final thoughts

Don’t create subdomains without a good reason.

Decide why you need them, what is a goal for creating them and how you are going to achieve them.

If you are an SEO master and got a website with subdomains to work on, analyze why they were created in the first place. Do they work well? Do they meet their initial purpose? Do they need to be more efficient?

Again, make sure you hide all the technical subdomains or those containing confidential information from the search engines.

And if you have a large enough workforce to maintain subdomains, go for it.

Share article
  1. Hey, Stasia!

    Thanks for putting this together – I had some doubts about subdomains and duplicate content before. Now it’s much more clear!

    Keep up the good work!

    1. Aggrey, I really appreciate your feedback! If you have any questions on the topic, don’t hesitate to ask 🙂

  2. wonderful. I was always confused by this, but the examples were really illustrative. I also appreciate the final thoughts. Exactly what I was looking for!

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