Subdomains give website owners the opportunity to branch away sites into new sites, a few years ago this was a really common practice when you had multiple sections of the site, be that a forum, careers page or perhaps a store. I tend to see the dynamics of sub-domains change recently, there are some websites which use proprietary software which often resolves on a subdomain, for example, a recruiter using job board software under a subdomain.
There is also the traditional protocol for a website, www, being classed as a subdomain with some sites deciding to show it whilst some do not – handling subdomains is a worthwhile task. Making an assessment is really important, especially if you are working with a site with a lot of history. There are also other considerations such as staging websites – which can often resolve within a subdomain if they can creep through and start to become indexed. As a rule of thumb, I always prefer to work with directories as opposed to subdomains, to try and encapsulate everything under one domain rather than branching. An example of this in the real world would be careers.example.com whereas I would prefer example.com/careers.
I typically start at a DNS level, as this is where you’d typically set up subdomains. You are telling browsers that when this particular URL is visited, it serves a particular directory or host. Skim through the DNS settings on your domain to see if there are any set-up and if they are still needed. You could theoretically check your FTP to see if there are any directories set up to facilitate a subdomain but this would create a blind spot for subdomains which reference other hosting locations/servers altogether. You’ll also find most other SEO crawling tools well versed in finding and assessing subdomains when they can find them. Occasionally, if there is no reference to a subdomain, an SEO tool may overlook it – this is why the DNS level assessment is key.
When you identify a subdomain you need to first make the assessment if that subdomain is providing real value to people who land on it. Occasionally you’ll find old subdomains there that haven’t been used for a long time nor updated if you switch these off and redirect them to a page on the main site explaining why it was shut down (for example) or the homepage. If the subdomain holds significant for functionality but you don’t want people to discover it nor find it in search engines, then I’d recommend updating the robots.txt file within the root of that subdomain FTP to handle this for you – or a global noindex, no-follow tag. If the subdomain is warranted, useful and a key part of the overall domain, I’d recommend taking steps to try and incorporate this into a directory rather than a subdomain typically.
I’d recommend using subdomains for very limited projects, this could be staging environments for websites, internal staff logins or perhaps some key functionality that needs to resolve on a dedicated subdomain. Regular validation of subdomains, and ensuring they are fit for purpose are key, I’d also recommend trying to use directories over subdomains wherever possible. If you do have subdomains setup, I’d also recommend running hygiene scans of the site with tools such as Screaming Frog, Sitebulb, SEMRush or ahrefs, as they can provide limited but useful guidance on subdomains (when they are able to find them).
Additional notes on subdomains.
- I would never recommend a subdomain for a client when it comes to SEO, if it needs to be used for sites that are not required to rank, fine – for everything else I try and move into a directory.
- If you branch your site by using a new CMS or new software, I’d always encourage clients to assess if they are comfortable with updating two platforms over the long term. It’s easier to make this assessment when a subdomain is in its infancy but over time
- Don’t forget you’ll likely need to set up a new robots.txt file, XML sitemap and GA profile for each subdomain for accurate reporting and SEO management.
- When setting up subdomains, if you are unfamiliar with DNS settings and setting a subdomain up; I’d recommend seeking professional help, setting errors at this level can take full websites offline.