An SEO audit is rarely limited to the www (or non-www) version of a website. When looking for potential duplicate content, it’s often important to know how many subdomains exist and, more importantly, how many of them are indexed by Google.
The good old search operators
An easy way to find indexed subdomains is to use search operators.
Start with “site:” and the root domain.
One by one, remove each subdomain (including: “www”) from the results with the “-inurl:” operator.
When there are no more results for Google to return, your query with the search operators should include all subdomains indexed.
However, this technique has its limits. It’s unlikely that the site you’re auditing has as many subdomains as wordpress.com, but you may come across a site with several dozen subdomains. This can potentially cause the following issues:
The process can be long, especially if it needs to be done for several domains.
You might get Google “captchas” along the way.
The size of queries is limited (around 30 keywords).