What is Localhost?
Localhost is the special network name that addresses your computer itself. Its equivalent address is 127.0.0.1.
Definition and Word Origin
"Local" means local, and "host" means host computer. A developer does not immediately upload the site to the internet; they first test it on their own computer using this address. Your computer acts as a server on its own. No one from the outside can see it, only you can see it.
How to Know and Use in Daily Life?
Web development: The address that opens in the browser after npm run dev.
Database: Locally installed Postgres or Redis connection.
API testing: Testing endpoints that have not been published yet.
Technical Depth and Architecture
What you need to know:
127.0.0.0/8: Loopback range, 127.0.0.1 is generally used.
Port: The port number on the same computer. If two applications bind to the same port, they will conflict.
The difference with 0.0.0.0: Localhost is only open to you, while 0.0.0.0 listens to everyone on the network.
Health check example:
curl http://localhost:3000/api/healthIf no response comes, the application is not running or the port is wrong. The firewall usually allows localhost traffic.
Frequently Mixed Things
It is thought to be a website. However, localhost is exclusive to your own computer and does not require a domain name or publishing.
Use in Different Disciplines
Theatre: A rehearsal room without an audience.
Music: Sound check before recording.
Kitchen: Tasting before serving.
Questions and answers
Why do we use localhost?
To fix errors securely on our own computer without exposing them to the internet.
What is 127.0.0.1?
It is the numeric equivalent of the localhost name. It represents the computer itself on every machine.
What is a port, and why is it needed?
It is a door number that separates applications on the same computer. It comes after the colon in the browser address.
Can it be accessed from the outside?
No. Publishing and a domain name are required for others to see it. Tunneling tools are used to share a test connection.
Related terms
Related tools
This explanation was written in plain language for TreScout with AI and machine-translated from the Turkish original · the Turkish version prevails. If something looks wrong or missing, write to hello@trescout.com. Read in Turkish →