The Loopback Address

Connecting to 127.0.0.1?

If you cannot reach 127.0.0.1, your system's hosts file or DNS settings might be misconfigured.

Try Opening 127.0.0.1:3000 →
Ping / Connectivity Check
ping -c 4 127.0.0.1

Fixing 127.0.0.1 Connection Refused

127.0.0.1 is the standard IP address for the loopback network interface. Connection failures here often point to deeper system configuration issues.

Hosts File

1. Missing Localhost Mapping

Your computer needs to know that "localhost" points to "127.0.0.1". Check your hosts file.

Windows (Run Notepad as Admin):
C:\Windows\System32\drivers\etc\hosts
# Ensure this line exists:
127.0.0.1       localhost
MacOS / Linux:
sudo nano /etc/hosts
# Ensure this line exists:
127.0.0.1       localhost

2. IPv4 vs IPv6

Modern systems also use ::1 for the IPv6 loopback. If 127.0.0.1 fails, try using [::1]:3000 in your browser to see if your server is listening on IPv6 only.

Developer Port Reference Guide

Frontend & Web
3000 React / Node / Default 3001 React Secondary
Backend & Infrastructure
5000 Flask / AirPlay 4000 Jekyll / Hexo
Database & Cache
3306 MySQL 5432 PostgreSQL
DevOps & Data Science
8888 Jupyter Notebook 9200 Elasticsearch 9090 Prometheus 15672 RabbitMQ UI 8500 Consul 127.0.0.1 Loopback IP