Free Tool
Online Port Checker
Test if ports are open, closed, or filtered on any server or website.
Port Scanner
Check if specific ports are open, closed, or filtered on a target host.
Common Ports Reference
FTP21
SSH22
Telnet23
SMTP25
DNS53
HTTP80
POP3110
IMAP143
HTTPS443
IMAPS993
POP3S995
RDP3389