Port Check
Test if a TCP port is open on any host. Check single ports or scan common ones.
About port checks
A port check opens a TCP connection to a specific port and reports whether it completes. Where ping tells you a machine answers, this tells you a particular service is listening and reachable: the distinction that matters when a database or an API is unreachable but the host pings fine.
Three outcomes are worth distinguishing. An open port completed the handshake: the service is up and reachable from outside. A refused connection means something answered but nothing is listening: usually the service is stopped. A timeout means nothing answered at all, which almost always points to a firewall silently dropping the traffic rather than a stopped service.
Frequently asked questions
- The port is open locally but closed from here. Why?
- A firewall, a security group or the service binding to 127.0.0.1 instead of 0.0.0.0. All three look identical from inside the machine and completely different from outside.
- Refused or timeout: which is worse?
- Refused is usually easier: the packet reached the host and nothing was listening. A timeout means the packet vanished, so you have both the service and the whole filtering path to investigate.
- Can I check a port on my home network?
- Only if it is reachable from the public internet. Private and loopback addresses are refused by design: scanning internal ranges from a public service is a security risk, not a feature.
- Does an open port mean I am exposed?
- It means the service is reachable. Whether that is a problem depends on what is listening and how it authenticates. A database or an admin port open to the world is worth closing today.