Open Port Checker: Test a Public TCP Port

How to Use This Tool

1. Enter a public hostname or IP address for a system you own or are authorized to test.
2. Enter one TCP port from 1 to 65535.
3. Run the check and distinguish a connection, refusal and timeout.

Choose the Target and Transport

Enter the public destination that outside clients actually use. A computer’s address such as 192.168.1.20 belongs to a private network and cannot be reached directly by this public checker. The target can also differ from the address shown on a router when the Internet provider places the connection behind carrier-grade NAT.

TCP and UDP are distinct transports even when their port numbers match. A successful TCP check on port 53 says nothing about DNS requests sent over UDP. This checker tests one TCP port at a time. Use a service-specific client when the task depends on an application response rather than a connection handshake.

Understand Each Result

An accepted connection means the tested address and port allowed the website server to complete a TCP connection during this attempt. It does not identify the application with certainty. Port 443 is commonly HTTPS, but a port number does not force the program listening there to be a web server.

A refusal commonly means the destination or an intermediate device actively rejected the connection. A timeout means no successful connection or explicit refusal arrived before the deadline. Filtering, routing problems, packet loss and an unavailable host can all produce a timeout. The result cannot locate the cause on its own.

Check Port Forwarding in a Useful Order

First confirm that the intended application is running and listening on the correct local interface. Next check the operating-system firewall. Then verify that the router forwards the external TCP port to the correct local address and internal port. A rule aimed at an old DHCP address can fail after a device reconnects.

Compare the router’s WAN address with the public address reported for your connection. A mismatch can indicate another router or provider NAT, although proxies and VPNs can also change the comparison. Do not open unrelated ports to chase a positive test. Remove temporary forwarding rules after the intended check.

Limits of an External Check

This request originates from the site’s hosting network. A service can allow that network and block another country or provider, or the reverse. Hostname results can also vary across IPv4, IPv6, geographic DNS and load-balanced addresses. Keep the resolved address and time beside the result.

A hosting firewall can prevent outgoing connections and make the measurement unavailable. Such a failure must not be presented as a closed target. Test only authorized systems. A port check does not audit passwords, encryption, vulnerabilities or the correctness of a game, mail or remote-access session.

• Diagnose ports, TLS certificates and CSRs

What the Result Means

This is a point-in-time TCP reachability check, not a UDP test, a vulnerability scan or proof that an application works correctly. Private and special-use targets are rejected.

Common Questions