Port Checker

About the Port Checker

Network ports are logical endpoints for communication. Every service that listens for incoming connections does so on a specific TCP or UDP port number — web servers on 80 and 443, SSH on 22, RDP on 3389, email (SMTP) on 25 and 587, and so on. This port checker attempts a TCP connection to a specific port on a remote host to determine whether it is open (accepting connections) or closed/filtered (blocked by a firewall or not listening).

Common port numbers and their services

• Port 21 — FTP (file transfer)
• Port 22 — SSH (secure remote shell)
• Port 25 — SMTP (server-to-server email delivery)
• Port 53 — DNS (domain name resolution)
• Port 80 — HTTP (unencrypted web traffic)
• Port 443 — HTTPS (encrypted web traffic)
• Port 587 — SMTP submission (email clients sending via provider)
• Port 3306 — MySQL / MariaDB database
• Port 3389 — RDP (Windows Remote Desktop)
• Port 5432 — PostgreSQL database
• Port 6379 — Redis cache
• Port 8080 — Alternative HTTP / common for development servers and proxies

Open vs closed vs filtered

• Open — A TCP connection was successfully established. A service is listening on that port and accepting connections.
• Closed — The host responded but indicated no service is listening on that port (TCP RST received).
• Filtered / timed out — No response received. This usually means a firewall is silently dropping connection attempts. The port may be open behind the firewall, or there may be no service listening.

To test multiple common ports at once and get a quick overview of a host's accessible services, use the Open Port Test tool.