About
Enter a public host and a port, and our server opens one TCP connection to it. That vantage point is the whole value: it answers whether the port is reachable from the internet, which is a different question from whether it works on your own machine.
How to use
Give a hostname or IP and a port number, then run. The result says whether the connection was accepted, refused, or timed out. Nothing is sent over the connection and it closes immediately.
Checking from outside your own network
Testing a port from the same network that hosts it proves almost nothing, because local traffic often skips the firewall entirely. The connection here starts on a public server, so it crosses whatever your provider, router, and host firewall do to strangers. That is why this is the check to run after configuring port forwarding, and why a success on your laptop is not evidence.
Accepted, refused, and no answer at all
Three outcomes, and they mean different things. Accepted means something completed a handshake on that port. Refused is an active rejection and usually means nothing is listening, which is a healthy answer from a machine that is up. No answer at all is the ambiguous one: a firewall dropping traffic silently looks identical to a host that does not exist. Read a timeout as filtered rather than closed.
The ports people usually bring here
443 and 80 to confirm a web server is exposed, 22 when SSH access has stopped working from outside, 25565 for a game server behind a home router, and mail ports when a provider is suspected of blocking them. Database ports such as 3306 and 5432 are worth checking for the opposite reason: if they answer from the public internet, that is the finding, and it should be closed rather than celebrated.
One connection, not a scan
Each run makes a single short connection to the one port you named. It does not sweep ranges, fingerprint services, or repeat on a timer, and it is not the tool to reach for if you want to enumerate what a host exposes. Point it at infrastructure you are responsible for, since probing someone else's host is their business rather than yours.
FAQ
Does an open port mean the service is healthy?
No. Accepting a connection is the first inch. A port can be open in front of a crashed application, an error page, or a login prompt you cannot pass.
Can it test UDP?
No, TCP only. UDP has no handshake to observe, so a UDP checker has to interpret silence, which is a different and much less reliable exercise.
It times out. Is the port closed?
Usually not. A closed port normally refuses fast. A timeout more often means a firewall is dropping the packet without answering, which is deliberate on most public hosts.
I forwarded a port on my router and it still shows shut. What next?
Confirm the device behind the rule is actually listening, then check whether your ISP places you behind carrier grade NAT, which makes inbound forwarding impossible no matter what the router says.
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