What is a localhost, and Why Is it Used?


Localhost is a term used in computer networking to describe the loopback address

This IP address refers to the local computer and is commonly used not only for local testing and debugging purposes but also for running networked apps locally.

A loopback address, for localhost, is a special IP address that directs network traffic back to the originating device. This means that when a request is sent to the localhost, it is redirected back to the local machine, rather than being sent to a remote server on the network.

When a user tries to access a website or application on their local machine, the request is redirected to apps and services running on their own computer.

This is useful for testing and debugging purposes, where it allows the user to use and test their applications and network configurations locally without having to connect to a remote server or network. This mechanism provides a safe and isolated environment for these tasks.

Important: No traffic targeted for IP ever gets on the actual physical network.

Using localhost For Testing and Debugging

The role of localhost in testing and debugging is significant, as it allows developers and network administrators to test and debug applications and configurations on their own computer before deploying them to a live server. By using the localhost, developers can quickly identify and resolve any issues that may arise in their applications, without having to worry about affecting live users or disrupting the network.

When an application is running on the localhost, developers can easily create targeted scenarios and test the application’s behavior in real-time with constraints in place which would be difficult in not impossible to make in a production environment.

Following are few examples of constraints that can be created locally to simulate different scenarios:

  • Network Constraints: These allow to simulate slow or unreliable network connections.
  • Storage Constraints: Running out of space, random hard drive disconnections and other scenarios can easily be created locally.

The user can see how the applications behave and then make necessary changes to the constraints to get to the expected application behavior.

In addition to being a useful tool for application development, localhost is also commonly used for testing and debugging network configurations. For example, network administrators can use localhost to simulate a network environment and test the behavior of different configurations, such as firewall rules or network security protocols, before deploying them to a live network.

How localhost connects to the network

Localhost is a special IP address ( that does not physically connect to a network. Instead, it serves as a loopback address that redirects network traffic back to the originating device. When a request is sent to the localhost, it is not sent to a remote server on the network but is instead redirected back to the local machine within the local networking stack.

However, just because localhost does not connect to a network in the traditional sense, it does not mean that it is isolated from the network. In fact, localhost can be used to access network services and resources that are running on the same machine.

For example, a web server running on the local machine can be accessed via the localhost, allowing developers to test and debug their web applications before deploying them to a live server.

What is Localhost Used for?

localhost can used for multiple purposes. Below are some real world examples.

Development and Testing

Localhost is widely used in the development of websites and applications, as it provides a convenient and safe environment for local testing and debugging. When a developer is building a website or application, they can run it on the localhost, allowing them to test the application’s functionality and behavior before deploying it to a live server.

The use of localhost for local development has several advantages. First, it allows developers to work on their projects offline, without having to worry about internet connectivity or slow connection speeds. This makes it easier for them to focus on the development process and make any necessary changes or adjustments to the application in real-time.

Second, localhost provides a safe and isolated environment for testing and debugging. Developers can test their applications and configurations on the localhost without having to worry about affecting live users or disrupting the network. This makes it easier for them to identify and resolve any issues with the application before it goes live, ensuring a smooth and reliable user experience.

Blocking External Domains, Websites and Applicatoins

One interesting use for the loopback address and localhost mechanism is by block applications by domain so they resolve to the address.

For example if you want to block your system from accessing a particular fishy domain badvirusdomain.com, the easiest way to do this is by enterting this domain name in your local hosts file. This way, if browser tries to access that websites the IP address will always resolve to, therefore blocking access to it.

The way this works is when the browser requests DNS for the IP address of the domain, the DNS server first looks for an entry in the hosts file and returns that to the browser. Only if the domain entry is not in the hosts file it contacts external DNS server for a domain to IP mapping.

Although there are better way of blocking websites or domain, but this process allows you to fine tune access that only affects a single machine.

Validating Network Functionality

One can open a command prompt or shell to run the ping command.

sohai@slap ~$ ping localhost

Pinging slap [::1] with 32 bytes of data:
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms

This send a request to the localhost and a success reply means your TCP/IP networking stack is working.

Benefits of Using Localhost

As I have shown above there are many advantges for using the loopback mechanism in terms of speed, reliability, security, and privacy.

When developing applications locally speed of the network connection is one of the main advantages when using localhost. Another benefit is that even when the external network goes down you can still continue with development and testing thus enhancing productivity.


Localhost is a great way to develop and test networked applications locally. You can use it to install application and web servers that requires a functioning network stack.

If you want to find out what is your public IP address then check our IP Tool showing your public IP address, location and ISP provider.