Covering the basics: Fully Qualified Domain Names (FQDN)

Fully Qualified Domain Names (FQDNs) play a crucial role in helping users and computers navigate the web seamlessly. FQDNs are an integral part of the Domain Name System (DNS). They serve as a human-readable representation of a specific location or resource on the internet. In this article, we will delve into the concept of FQDN.

Exploring what they are, how they work, and why they are essential for the functioning of the internet. Let’s get the most important out of the way first. Here is an example of what a Fully Qualified Domain Name looks like, and what the character limit is.

How many characters can a fully qualified domain name can contain?

Max length is 255 characters. Since so many characters are pointless… And there are people with a sense of humor, here’s how this looks like in practice.


 Domain prefix registration of more than 63 characters is allowed with a new TLD of more than 13 characters.

Previous record holder was a village in Wales, Great Britain on the Isle of Anglesey.

Longest domain name

If this has you scratching your head, open the website and read what it’s about.

Why only 63 characters, and not 255?

  1. The name (the part between the dots) technically has a maximum of 63 characters
  2. The entire fully qualified name (e.g. can have a maximum of 255 characters

Now that we’ve scratched the surface, let’s dive deeper.

Understanding FQDN:

FQDN - abbrevation for Fully Qualified Domain Name
There is wood cube with the word FQDN. It is an abbreviation for Fully Qualified Domain Name. Source: Shutterstock

FQDN stands for Fully Qualified Domain Name. To grasp its meaning, let’s break down the term:

  1. Domain Name: A domain name is a human-readable label that represents a specific IP address or a group of IP addresses on the internet. It is a crucial component of web addresses, helping users access websites easily.
  2. Fully Qualified: The term “fully qualified” indicates that the domain name is complete and includes all necessary information to locate the resource accurately.

An FQDN comprises three main parts:

  • Host Name: This is the actual name of the specific machine or resource on the internet, such as “www” for a website or “mail” for an email server.
  • Domain Name: This is the middle part of the FQDN and represents the larger organization or network to which the host belongs. For example, in “,” “example” is the domain name.
  • Top-Level Domain (TLD): This is the last part of the FQDN and usually indicates the type or purpose of the resource. Common TLDs include “.com,” “.org,” and “.net.”

Putting it all together, an FQDN looks like this: hostname.domainname.tld.

How a FQDN Work:

When a user enters a web address into a browser, the FQDN is translated into an IP address by the DNS. The DNS is a distributed database that translates human-readable domain names into machine-readable IP addresses, facilitating the seamless communication between computers on the internet.

Here’s a simplified step-by-step process of how FQDNs work:

  1. User Input: A user enters an FQDN (e.g., ““) into a web browser.
  2. DNS Lookup: The browser sends a request to a DNS server to translate the FQDN into an IP address.
  3. Resolution: The DNS server searches its database for the corresponding IP address of the FQDN.
  4. Response: The DNS server returns the IP address to the browser.
  5. Connection: The browser establishes a connection to the server using the obtained IP address. This enables the retrieval of the requested web page.

Importance of FQDN:

FQDNs are essential for various reasons:

  1. Human-Readable: FQDNs provide a user-friendly way of accessing resources on the internet. They make it easier for people to remember and navigate websites.
  2. Network Organization: FQDNs help organize and categorize resources within a network, allowing for efficient management and maintenance.
  3. Global Standard: FQDNs adhere to a global standard, ensuring consistency and interoperability across the internet.


Fully Qualified Domain Names (FQDNs) are the building blocks of the internet. They serve as the bridge between human-friendly addresses and machine-readable IP addresses. Understanding FQDNs is crucial for anyone navigating the web, as they play a pivotal role in the seamless functioning of the internet infrastructure.


Goran Duskic has been the Founder and CEO of WhoAPI Inc. since 2011, a company that specializes in developing APIs, including the well-known Whois API. He started his career in internet entrepreneurship in 2006 and has co-founded several online businesses, including a web hosting company that he later sold. Goran's work primarily involves creating practical API solutions to meet technological needs.