Port Check answers a simple question: is a specific TCP port accepting connections on a given host from the public internet? It opens a single TCP socket from our server to host:port and reports the outcome within three seconds.
How to read the result
- OPEN — the 3-way handshake completed. Something is listening there and accepting connections.
- CLOSED — the host replied but rejected the connection (RST). The host is up, nothing is listening on that port.
- FILTERED — no reply at all within the timeout. A firewall is silently dropping packets.
FAQ
Why is my port filtered but works locally? Your ISP, your home router or a cloud security group is blocking inbound connections. Open the port in the router / security group configuration.
Does this work for UDP? No. This tool tests TCP only. UDP has no handshake, so "open" for UDP requires application-level probing.
Is this the same as nmap? Nmap scans a list of ports at once and does service fingerprinting. Port Check targets a single port and is 10× faster for the common "is it open?" question.