Online Port Checker
Check whether a TCP port is open on a server or website. Handy after configuring a firewall, setting up port forwarding or launching a new service.
How the open port check works
The tool opens a TCP connection to the host or IP you enter on every port in the list (separate multiple ports with commas, up to 12 at a time) and reports the result: open or closed, plus the connection time in milliseconds. Crucially, the check runs from an external server, not from your computer. That matters: a local firewall, antivirus or router settings can give you one answer, while from the outside, where your real users are, the port may look completely different. Only an external check tells you whether a service is reachable from the internet.
Common ports and what they are for
These are the ports people check most often:
22 | SSH: remote server administration |
80 | HTTP: unencrypted web server |
443 | HTTPS: web server over TLS |
25 | SMTP: sending email |
3306 | MySQL: database |
5432 | PostgreSQL: database |
6379 | Redis: key-value store |
Why you should close unused ports
Every port exposed to the internet is a potential entry point. Databases such as MySQL, PostgreSQL and Redis should normally listen only on localhost or a private network, not be reachable from the internet: an open 3306 or 6379 is a regular target for automated scanners. A typical use for this tool is verification after a firewall change. You tighten a rule in iptables, ufw, firewalld or your provider's cloud firewall, then immediately confirm from the outside that the port is no longer reachable while the one you need (say, 443) is still open. That way you know the configuration took effect before your users notice anything. Note that many VPS and cloud providers block outbound port 25 on new accounts by default to fight spam.