What is a port checker?
Every service on a networked device listens on a numbered port. Web servers use port 80 for HTTP and 443 for HTTPS. SSH is on 22. MySQL is on 3306. When you can't reach a service, the first thing to check is whether the port is actually open.
This tool tries to open a TCP connection from our server to each port you specify. If the connection succeeds, the port is open. If it times out or gets refused, it shows as closed. That could mean nothing is listening, or a firewall is dropping the packets.
Common port reference
21 FTP · 22 SSH · 23 Telnet (insecure) · 25 SMTP · 53 DNS · 80 HTTP · 443 HTTPS · 587 SMTP/TLS · 993 IMAPS · 995 POP3S · 3306 MySQL · 3389 RDP · 5432 PostgreSQL · 6379 Redis · 27017 MongoDB
Questions we get a lot
What is the difference between open and closed?
Open means something is actively listening on that port and our server was able to connect. Closed means either nothing is listening, or a firewall dropped the connection before it got through.
Why is my web server port showing as closed?
Usually one of three things: a firewall or cloud security group is blocking it, the service isn't running, or it's running on a different port than expected.
Is this a full port scan?
No. It only tests whether a TCP connection can be established. It doesn't perform any reconnaissance, banner grabbing or vulnerability scanning.
Which ports should not be open to the internet?
Database ports like 3306, 5432, 6379 and 27017 should never be publicly accessible. Telnet (23) is unencrypted and should always be replaced with SSH. RDP (3389) should be behind a VPN or restricted to specific IPs.