Open Port Checker
Check if a port is open or closed on any host.
Port checking is performed from an external server, not your local machine. Results reflect whether the port is reachable from the public internet.
Frequently Asked Questions
What does it mean if a port is open vs closed?
Open: a service is actively listening on that port and the firewall allows connections — the tool gets a response. Closed: the host is reachable but nothing is listening on that port (or the firewall actively rejects connections). Filtered/timed out: the host may be unreachable or a firewall is dropping packets without responding.
What are the most important ports to know?
Common ports: 21 (FTP), 22 (SSH), 25 (SMTP email), 53 (DNS), 80 (HTTP), 110 (POP3), 143 (IMAP), 443 (HTTPS), 465/587 (SMTP with SSL/TLS), 3306 (MySQL), 3389 (RDP/Windows Remote Desktop), 5432 (PostgreSQL), 6379 (Redis), 8080/8443 (HTTP/HTTPS alt), 27017 (MongoDB).
Why would a port be open on my server unexpectedly?
An open port you don't recognise could indicate: a service installed by software running on a non-default port, a misconfigured firewall, or potentially unwanted software. Investigate with netstat (Windows/Linux) or lsof -i (macOS/Linux) to identify which process is listening on the port.