Why can't browsers check ports directly?

For security reasons, JavaScript in browsers runs in a sandbox environment and cannot establish TCP/UDP connections directly. Port checking requires OS-level network calls, so this tool generates commands for you to run in your terminal.

What's the difference between nc, nmap, and telnet?

nc (netcat) is lightweight and fast for single port checks. nmap is the most powerful, supporting batch scans, service detection, and OS detection. telnet is a classic tool — connection success indicates an open port. curl only works for HTTP/HTTPS services.

Why is a port open but the service inaccessible?

An open port only means a program is listening on that port. The service itself may have issues: firewall rules restricting specific IPs, misconfiguration, or intermediate network devices blocking traffic. Check firewall rules and service logs.

Which ports should not be exposed to the internet?

General rule: database ports (3306, 5432, 6379 etc.), cache ports (11211), and internal management ports should not be exposed. Only open necessary web service ports (80, 443). Access other services via VPN or SSH tunneling.

Port Check

Check Port Open Status

Target Address

Port Number

Common Ports Quick Select

Common Ports Reference

Port	Service	Description
`80`	HTTP	Default web server port
`443`	HTTPS	Encrypted web traffic, SSL/TLS
`8080`	HTTP Proxy	Common web proxy/alternate HTTP
`8443`	HTTPS Alt	Alternate HTTPS, often admin panels
`3000`	Node.js	Node.js default port
`8000`	Django/Python	Python web dev common port
`9090`	Prometheus	Prometheus monitoring default

⚠️ Port Security Tips

Only scan servers you are authorized to test. Unauthorized scanning may be illegal.
Close unnecessary ports in production — follow the principle of least privilege.
Database ports (3306, 5432, 6379 etc.) should not be exposed publicly; access via SSH tunneling.
Use firewalls (iptables, ufw) to restrict port access by source IP.
Regularly audit open ports and close unused services.
Change the default SSH port 22 to a non-standard port to reduce brute-force attacks.

Port Check Tool Guide

Key Features

Command Generation - One-click generation of nc, nmap, telnet, curl commands
Common Ports - Quick select from 9 common service ports
Batch Check - Check multiple ports at once
Port Reference - Browse common ports by category

Use Cases

Verify ports are listening after deployment
Troubleshoot network connectivity issues
Security audit for port exposure
Confirm firewall rules are working