There are domains, and there are subdomains. To those unfamiliar with subdomains, they are subdivisions of a primary domain. So if is your domain, then is a subdomain. Together, they make up the domain infrastructure of your company.

As you have probably inferred from the title of this piece, subdomains are a massive target for hackers who are trying to crawl into your company infrastructure and disrupt it, or steal information.

That is why protecting your subdomains should be one of your primary concerns. If you are a security engineer or a website owner, knowing how to find subdomains can help you in your job. There are many ways to monitor your domain infrastructure and observe subdomains of other companies. In this article, we will discuss what these subdomains are, the most common threats, and how to avoid them.

What is a Subdomain?

Subdomains, also called subsets, are a smaller part of a larger domain. They can be utilized to organize your existing website into a whole separate site. Most frequently, subdomains are used for the content which is distinctly different than the one found on the domain site. You can identify a subdomain by the website URL: they look something like “,” with an additional section left of the root URL.

Let’s dive further to explore the concept of subdomains by breaking down a domain name.

A full domain name includes two sections: Top-level domain (TLD), and Second-level Domain (SLD).

The TLD can be found right after the name of the site – in this case, .com is the TLD. As you may know, there are many types of TLDs, with the most common being .com, .org, and .net.

After that, we have the SLD, which can be found one step left from the TLD. In this case and most others, this is the name of your website. You get to choose your website name and SLD, therefore making each domain name unique.

Now the final part, right after the website name, is the subdomain of that website.

Fun fact: WWW. is also aa subdomain, but you are not forced to use it for your sub. You may replace it with almost any word, creating a subdomain with an entirely original web address. In many countries, you can tell what kind of website it is by seeing the subdomain letters. For example, in the United Kingdom, is usually some education facility, while will be a Ministry of Defense or HM Forces public site.

Ways of Finding Subdomains

Before delving into finding subdomains, it’s essential to understand why this can help your business maintain the right level of online security.

Owning a subdomain that is unsecured can be a severe threat to your business, its reputation, and your customer loyalty. There have been many incidents recently where the attacker used various subdomain tricks to disrupt a company’s infrastructure. We will not dive into all the threats and vulnerabilities of exposed subdomains in this article, but you can find this information online. Instead, we will focus on how you can protect yourself by monitoring your subdomains becoming less vulnerable to attacks.

Terminal-based Subdomain Scanners

One of the simplest ways to find subdomains is by using terminal-based subdomain scanners. Let’s take aa closer look at one called This is a python-based tool, API wrapper, and command-line client for all the various tools hosted on Using will give you access not only to the terminal subdomain finder, but also the other six spyse tools which will help you maintain an adequate level of security for your company online.


This is another Python subdomain scanner tool which helps infosec researchers greatly. It does a full DNS zone transfer and can even run a query against the VirusTotal subdomain database.

For its simplicity, Knock does a fantastic job when you need to find subdomains.

Using terminal-based subdomain scanners can be time-consuming and not very comfortable for people with limited knowledge in the field. You will have to spend some time to structure collected information, and it can be a hassle. That’s why using online subdomain finders is the more recommended and relaxed way to find subdomains of a domain.

Online Subdomain Finding Tools

Using online subdomain scanners is the most laid-back and efficient way to explore subdomains. The new tool on the market, FindSubdomains, is straight-up the fastest way to perform daily sub reconnaissance. This tool uses a self-developed subdomain finder to collect immense amounts of data and store it in a dynamic database. So when you ask it to fid all subdomains of a domain, you don’t have to wait at all. This app does it by proxy every day and gives you conveniently structured data at any time. You can also get IP numbers, Geo, and AS numbers to enrich your data.

This tool is a blessing for system administrators, security engineers, pen-testers, and business analysts. Not only does this subdomain finder make their job more comfortable, but it also helps you monitor the cybersecurity of your company with little to no technical knowledge.

As stated earlier, Findsubdomains is just one small part of the Spyse ecosystem. There are six other useful tools that you get access to as a newly registered user on Spyse. All new users get three credits for free to test out all the services Spyse has to offer. Rest assured this is the best way to find subdomains of a domain — do not hesitate to try it on yourself!