Port Scanner
TCP probes against common port groups — only for targets you own or are authorized to test.
What a port check does
A TCP connect probe tells you whether a service is listening on a port: 80/443 for web, 25/465/587 for mail, 3306/5432 for databases, 22 for SSH. Open ports are your attack surface — every one should be intentional, firewalled and patched.
Authorization matters
Port scanning hosts you do not own can violate terms of service and local law. This tool requires an explicit authorization confirmation and only probes common service port groups — use it on your own servers.
Closed vs filtered
A closed port answers with RST (nothing listens). A filtered port gets no answer at all — a firewall dropped the packet. From the outside, filtered is what you want for services that must not be public.
Need the in-depth Chinese version? Read the full guide.
Related articles
A Beginner's Guide to Port Scanning: Audit What Your Server Exposes
How to confirm your server's exposed ports match expectations after deployment: the principles of port scanning, what the three result states mean, and the right way for admins to self-audit.
"The TCP Three-Way Handshake and Latency: Why Pages Stay Slow Despite High Bandwidth"
"500 Mbps connection, yet pages take 3 seconds to open? Bandwidth is only one dimension of network experience — round-trip latency and handshake count are often the real culprits. How TCP handshakes, RTT, and page loading fit together."
Where Cross-Border Latency Comes From: Submarine Cables, Detours, and Congestion
Why does Singapore to the US start at 160ms physically? Breaking down the four sources of cross-border network latency — the speed of light and cable paths, routing detours, congestion queuing, device forwarding — plus how to use ping to pinpoint which segment is at fault.
Why Your Proxy Gets Detected: A Look at IP Disguise
Why sites still recognize you behind a proxy: the full toolkit of detection methods — datacenter IPs, ASN flags, blacklists, consistency signals — and how to test your own disguise score.
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Frequently asked questions
Why does the scan require confirmation?
To ensure you only scan targets you own or are authorized to test. Unauthorized port scanning is illegal in many jurisdictions.
My port shows closed but the service works?
If a service only binds to localhost or a private interface, it is invisible from outside — that is correct behavior for databases. Public web ports failing while the site works may indicate geo-blocking of our scanner IP.
How fast is the scan?
Common port groups complete in a few seconds. This tool is intentionally limited to service groups rather than all 65535 ports.