Port Checker
Test whether common or custom TCP ports are open on a host.
Frequently asked questions
What does the port checker do?
It tests whether specific TCP ports are open (accepting connections) on a public host — useful for confirming a service is reachable or a firewall change worked.
Which ports does it check by default?
A set of common ports including 21, 22, 25, 53, 80, 110, 143, 443, 465, 587, 993, 995, 3306, 3389 and more. You can also enter your own comma-separated list.
Can I scan any host?
Only public, internet-routable hosts. Private and reserved addresses are rejected, so the tool cannot be used to probe internal networks.
What is the difference between an open, closed and filtered port?
An open port accepts connections, a closed port actively refuses them, and a filtered port gives no response at all because a firewall is dropping the packets. This tool reports whether a connection succeeded.
Why does a port show as closed when my service is running?
Common causes are a firewall blocking the port, the service listening only on localhost rather than the public interface, network address translation not forwarding the port, or the service bound to a different port.
What is the difference between TCP and UDP ports?
TCP is connection-oriented and used by most services like web and email, so its ports can be tested by attempting a connection. UDP is connectionless, which makes open or filtered states much harder to distinguish.
Which common ports should I know?
Frequently used ones include 22 for SSH, 25, 465 and 587 for SMTP, 53 for DNS, 80 and 443 for web, 110 and 995 for POP3, 143 and 993 for IMAP, and 3306 for MySQL.