Port Scanner Guide

A port scan sends connection attempts to TCP/UDP ports on a host to learn which services are listening. Security teams use authorized scans; attackers use them for reconnaissance.

TCP connect scan completes the handshake. SYN scan sends half-open probes. UDP scans are slower because many ports drop packets silently. Service/version detection follows open ports.

Scan only systems you own or have written permission to test. Many jurisdictions treat unauthorized scanning as illegal access. Cloud providers may suspend accounts for probing external hosts.

Use the Port Reference tool for well-known port numbers. Test local services with curl or your app health endpoint. For production, rely on internal monitoring—not ad-hoc scans from a browser.

Port Reference lists IANA-style service names. HTTP Request Builder tests a single endpoint. SSL Checker validates certificates on a known HTTPS URL.