Port Checker

Port Checker attempts a connection to about twenty well known ports on a host at once, covering common services like SSH, HTTP, HTTPS, SMTP, MySQL and RDP, and reports each one as open, closed or filtered.

This is useful for confirming a firewall rule actually took effect after changing it, checking that a database or admin service you meant to keep private is not sitting open to the internet, or getting a fast overview of what a server is running before digging further.

This checks a fixed list of common ports, not an arbitrary port or a full range scan, by design, since an open-ended port scanner on a free public tool would be an easy way to turn it into a scanning proxy against someone else's server. Filtered means no response came back at all, which usually means a firewall is silently dropping the connection rather than actively refusing it.