Port Check

Test if a specific TCP port is open and accepting connections on any host or IP address.

Frequently Asked Questions

Common questions about the Port Check tool.

A TCP port is a numbered endpoint on a server where a specific service listens — e.g. 80 for HTTP, 443 for HTTPS, 22 for SSH. Checking a port tells you whether a firewall, ACL, or service is allowing external connections to that port.

The most common causes are: (1) firewall blocking inbound traffic, (2) the service is bound to 127.0.0.1 only, not 0.0.0.0, (3) a network-level ACL or security group blocking the source IP, or (4) the service crashed or is restarting.

Checking a single port on a publicly-exposed server is generally fine, but full port scans can violate acceptable-use policies or laws in some jurisdictions. Only scan systems you own or have explicit written permission to test.

Open means the service is accepting connections. Closed means the port is reachable but no service is listening. Filtered means a firewall is silently dropping the packet — you get no response at all.

No — UDP port checks are unreliable over the internet because UDP is connectionless. This tool only checks TCP. For UDP, use a local nmap -sU scan from an authorised host.