Open ports are doorways into a server. Each one that’s exposed but unneeded is a potential entry point for attackers. Our free Port Scanner checks a host for common open ports and identifies the services behind them — scan only hosts you own or are authorized to test.
Open, closed, and filtered
An open port is accepting connections (a service is listening). A closed port is reachable but nothing is listening. A filtered port gives no response — usually a firewall is dropping the traffic. Knowing the difference helps you tell a misconfiguration from a deliberate block.
How to scan and what to do next
Open the Port Scanner, enter a hostname, and review the open ports. Close or firewall anything you don’t need — exposed databases (MySQL, PostgreSQL, Redis, MongoDB) and remote-access ports (RDP, SSH) are common risks. For a broader review, pair it with our Security Header Scanner and SSL Checker.