Port Checker
Test whether a TCP port on a public hostname or IP address is reachable from the internet.
Check a TCP port
How does the port checker work?
The tool attempts a TCP connection to the selected port. An open result means the target accepted the connection from our server.
A closed or filtered result can also be caused by a firewall, network rule or service that only accepts connections from specific locations. Private and local network addresses are not supported.
When to use an online port checker
A port checker is useful after changing firewall rules, forwarding a router port, publishing a web service or troubleshooting a server that should be reachable from the public internet. It tests from outside your local network, which is important because a service can work internally while still being blocked for external users.
Common examples include checking port 80 or 443 for web servers, port 22 for SSH access or a custom application port after deployment. If the port appears closed, review the service status, host firewall, cloud security group, router forwarding rule and whether the service binds to the correct public interface.
Why can a port look closed when the service is running?
Firewalls, provider rules, NAT configuration and allowlists can block external connections even when the application is running locally. Some services also accept traffic only from specific IP ranges.
Can this test private IP addresses?
No. Private and local network addresses are not useful for a public server-side check and are intentionally rejected.