If you work in the tech space or are just starting to learn website development and web hosting, you may have seen the term “localhost” here and there. It’s an example of technical jargon that might seem obscure at first. However, it’s actually not too difficult to grasp if you have the background knowledge.
In this quick guide, we’ll tell you what you need to know to start using localhost in your projects. We’ll explain what the term means, why it exists, and how IT professionals utilize it in their day-to-day.
What is localhost?
Localhost is a hostname that refers to the local machine currently making the request. On many computers, localhost is an alias for the IP address 127.0.0.1. When a computer pings this IP address, it is communicating with itself. Localhost is useful for software testing and security purposes independent of a larger network.
We realize that's a lot to take in. So, let’s unpack this definition, starting with IP addresses: What are they, and why are they important?
What is an IP address?
To visit a website, you enter that website’s domain name into your browser bar — for example, hubspot.com.
But, a domain name alone doesn't identify a website. Rather, a domain name is simply an alias for a website’s IP address, a combination of numbers that identifies a device on a network. An IP address is made up of four numbers, each between 0 and 255. For example, the IP address associated with the server that hosts HubSpot's website is 188.8.131.52. Every device has a unique IP address, even your PC.
When you punch “hubspot.com” into your browser bar and hit enter, the Domain Name System (DNS) takes what you entered, sees that it's paired with the IP address 184.108.40.206, and routes your request to the right place, HubSpot’s web server. The reality is a bit more complicated, but that's the gist.
Of course, we don’t need to know the IP addresses of our favorite websites, or even what IP addresses are, because of domain names — it’s much easier to remember and type “hubspot.com” than four individual numbers.
What is a loopback address?
IP addresses can identify individual servers on the internet, as well as devices outside of the internet on local networks. Whenever a new networked device is created, it gets an IP address.
However, some IP addresses are reserved for certain reasons. For instance, all addresses beginning with the number “127” are special IP addresses called “local loopback addresses.” Instead of identifying another device on the internet, a loopback address references a device on your private, local network. This is why no website may have an IP address starting with “127.”
Loopback addresses can’t be reached by outside devices. When you send a request to a loopback address, this triggers a loopback, meaning the request is sent back to the server it came from. As a result, loopbacks don’t go through the internet — they stay in your local network.
Now that we understand IP addresses and loopbacks, we can turn our attention back to localhost.
What does localhost mean?
When it comes to computer networks, localhost is like a secret code that refers to the very computer you are using. Think of it as a way of saying "this computer." It serves a purpose when you make a special request to your own device, known as a loopback request. These requests are handy for testing and security purposes, as we'll explore later.
Typically, you can access the localhost of any computer through a loopback address called 127.0.0.1. By default, this IP address points to a server that is running on the same device. So when your computer asks for the IP address 127.0.0.1, it's essentially making a request to itself, its "local host."
The term "localhost" also functions as the domain name for the loopback IP address 127.0.0.1, similar to how "hubspot.com" stands in for the IP address 220.127.116.11. However, there's an important distinction: If you type "localhost" into your browser, your request won't travel through the internet. Instead, it will loop back and end up right back on your computer.
No matter which device you're using, a request to 127.0.0.1 or "localhost" will always be sent back to the same device you're working on. The best part is that you don't need any special permissions or equipment for this to happen. The computer's operating system is designed to act as a server and handle loopback requests seamlessly.
One more quick note about localhost: 127.0.0.1 is the default IP address for localhost in IPv4. In IPv6, the default localhost address is ::1. Learn more about what IPv4 and IPv6 mean here.
What is localhost used for?
Okay, being able to make requests to your own computer is interesting and all, but what can it be used for? As it turns out, mostly testing. Here are its common uses:
Website and Web Application Testing
When you're in the process of building a website, it's important to test how it looks and functions in a web browser. However, you might not want to make your unfinished website live and accessible to the public just yet. This is where localhost comes in handy.
By hosting your website files on your personal computer and making them available via localhost, you can access your website through your web browser and simulate the experience of visiting it from a remote device. The best part is that everything stays on your computer and remains private.
This is a common practice among application and web developers who use localhost as a private testing server for their websites and applications. It allows them to test programs without the need to send files through the internet, making it more secure and ensuring that their website is not exposed to the public before it's ready.
Network and Speed Testing
IT staff and system admins can also use localhost to test the the local network without requiring an internet connection — they just need to send a request to localhost and monitor this request to ensure that the system’s software and hardware are working. Admins can also evaluate the speed of these requests to determine if optimizations should be made.
Blocking Bad Websites
Additionally, network administrators have the ability to redirect requests for known malicious websites to localhost in order to protect their networks from potential attacks. This can be achieved by modifying the computer's hosts file, which contains a list of domain names and their corresponding IP addresses. In the past, the hosts file was responsible for converting domain names to IP addresses before the introduction of the Domain Name System (DNS). Although it is now considered outdated, hosts files can still be found on modern computers.
To prevent accidentally accessing harmful websites, administrators can add the domain of the website to the hosts file and assign it to the IP address 127.0.0.1. As a result, when the user enters the domain in their browser, they will be safely redirected to localhost instead of the actual website. There are numerous pre-made hosts files available online, eliminating the need for administrators to start from scratch.
There’s no place like 127.0.0.1.
A popular saying in the tech world goes, "There's no place like 127.0.0.1." It's a clever play on the phrase "There's no place like home," highlighting the significance of localhost as the "home" device. This joke helps us understand the importance of localhost as a safe haven for running tests without relying on the internet.
It serves as a home base, allowing you to experiment and perfect your creations before unveiling them to the world. While pinging localhost may not be a daily activity for non-IT professionals, understanding its role can simplify the testing process and remove some of the mystery surrounding it.