Online Nmap Port Scanner

About Nmap Port Scanner

Only scan hosts you own or have written permission to test. A port scan is how an attack begins, and scanning somebody else's systems without permission can break the law where you are and the terms of the network you are on. This tool refuses private and internal addresses outright, scans one host at a time, and allows five scans every ten minutes.

It works the way nmap -sT does: a full TCP connection to each port, from this site's server. A port that completes the handshake is open; one that answers with a reset is closed; one that does not answer before the timeout is filtered — almost always a firewall dropping the packet. The presets are Nmap's own: the 20 ports it finds open most often (--top-ports 20), or the 100 its fast scan checks (-F). Or give your own list, with ranges, up to 100 ports.

With version detection on, each open port is asked what it is, as nmap -sV does. SSH, FTP, SMTP, POP3 and IMAP introduce themselves; a web server is asked for its Server header; a TLS port gets a handshake first, and the negotiated TLS version is shown; MySQL's binary greeting is read for its version. What a service says is what it claims — a banner can be changed or hidden — so treat it as a lead, not proof.

The result is a table with the open ports first, and the same scan written out the way Nmap prints one, ready to paste into a ticket.

Where it helps

• Nmap's own top-20 and top-100 port lists, or your own ports and ranges.
• Nmap's states — open, closed, filtered — so the results read like the tool people already know.
• Version detection: SSH, mail and FTP banners, web Server headers, TLS versions and MySQL versions.
• Output in Nmap's own format, alongside the table, for reports and tickets.
• Refuses private, internal, cloud-metadata and multicast addresses, and is rate-limited so it cannot be used to scan at scale.

Limits

• A TCP connect scan only: no SYN, UDP, OS detection or scripts, which need raw sockets this server does not have.
• At most 100 ports per scan and five scans every ten minutes, deliberately.
• The scan comes from this site's server, not your machine, so it shows what the internet sees — not what your own network can reach.
• A firewall that rate-limits or tarpits connections can make open ports look filtered.
• Banners are what a service claims; they can be changed, hidden or faked.

Frequently asked questions

Is it legal to scan a port?

Scanning your own systems, or systems you have written permission to test, is normal security practice. Scanning anyone else's can be unlawful depending on where you are, and it breaks most networks' terms of use. When in doubt, ask first — or use scanme.nmap.org, which exists to be scanned.

What is the difference between closed and filtered?

Closed means the host answered and said nothing is listening there — it sent a TCP reset. Filtered means nothing answered at all before the timeout, which almost always means a firewall dropped the attempt. Closed tells an attacker the host is up; filtered tells them much less.

How is this different from running nmap?

It does Nmap's TCP connect scan (-sT) of its top-port lists with version detection (-sV), from this site's server. Nmap itself can also do SYN, UDP and OS-detection scans and run scripts, and from your own machine it can reach your private network, which this deliberately cannot.

Why does a port I know is open show as filtered?

Because something between this server and the host dropped the connection: a firewall that only allows certain source addresses, a provider that blocks the port, or a rate limit. The scan comes from the internet, so it sees what the internet sees.

Related tools

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