Open Port Checker

What the port checker tests

Enter a hostname or IPv4 address and one TCP port. Our server resolves the name through public DNS, then opens a single TCP connection to that IP and port and waits up to 5 seconds for the handshake. If the service speaks first (SSH, SMTP, FTP and many others send a greeting), the first 256 bytes are shown as the banner. Nothing else is sent to the server.

How to read the result

• Open: the TCP handshake completed, so a program is listening and the firewall lets our server through. The connect time is roughly one network round trip between our server and the host.
• Closed: the host answered with a TCP reset. The machine is reachable, but no service listens on that port, or a firewall rejects the connection instead of dropping it.
• Filtered: no answer within 5 seconds. A firewall (host firewall, cloud security group, router) is most likely dropping the packets, or the host is offline. A "host unreachable" detail means a router reported that the address cannot be reached.

Common problems

• Open locally, filtered from here: the service may listen only on 127.0.0.1, or a cloud security group, ufw/iptables rule or the router does not forward the port. Check with ss -tlnp that it listens on 0.0.0.0 or the public address.
• Port forwarding at home: test your public IP (see IP Info), not the 192.168.x.x address. Many ISPs block inbound 25, 80, 445 and use CGNAT (100.64.0.0/10), which makes inbound connections impossible without a tunnel.
• UDP ports: this tool tests TCP only. UDP services such as DNS, WireGuard or game servers do not complete a handshake, so a simple connect test cannot tell open from filtered.
• Different results from different places: some servers allowlist source IPs or rate-limit scanners, so the result from our server can differ from yours.

Limits

Only public IPv4 addresses can be tested; private, loopback, link-local and cloud metadata addresses are refused. One port per check, and each visitor can run up to 10 checks per minute. For what a port is used for and whether it should be exposed, see the port number reference.