Pro move: type dmarc:yourdomain.com or blacklist:1.2.3.4 straight into the box — it switches tools for you.
About this tool. Opens a raw TCP connection to any host and port from our edge and times the handshake. Handy for checking whether a service is reachable at all. Ports 80/443 are reserved for the HTTP checks, and port 25 is blocked platform-wide — the SMTP tool covers mail servers.
How to read your open port checker results
We open a TCP connection to the host and port you give and report whether it is open and how quickly it responds.
Open means something is listening. Closed or timed out means nothing is answering, or a firewall is blocking it.
Common problems and how to fix them
A service should be reachable but the port is closed
Check the service is running and bound to the right interface, and that no firewall or security group blocks the port.
Common questions.What does a port test do?
It checks whether a specific TCP port on a host accepts connections, and measures the connect time.
Why is a port showing as closed?
Either nothing is listening on that port, or a firewall is dropping the connection before it completes.