NETCONFIG

Port Checker

Verify if a TCP port is open and accepting connections on a remote server.

Common:

TCP Reachability Probe

Enter an IP or hostname and port above to test reachability from edge network nodes.

About the port checker

Check whether a TCP port on a host is open from the internet. It is an online port checker, handy for testing port forwarding, firewall rules and whether a service such as SSH, HTTPS or a game server is reachable.

Also searched as: open port checker · port scanner online · TCP port test · check if port is open · port forwarding test · port status checker · is my port open

Open, closed or filtered

Open means a service answered. Closed means the host replied that nothing listens on that port. Filtered or timed out usually means a firewall silently dropped the packet. The check completes a real TCP handshake and reports its latency.

Testing port forwarding

After creating a forwarding rule on a router, check the port against your public IP. If it shows closed, confirm the service is running, the rule points to the right internal address, and the host firewall allows it. Carrier-grade NAT makes inbound ports impossible on some home connections.

Is it safe to leave it open?

Our port reference lists what each common port is for and whether it should face the internet. Databases, remote desktop and file sharing are common targets; keep them behind a VPN.

How this tool works and how to read the results

What this tool does

Attempts a real TCP connection to the host and port you specify from our server, and reports whether it succeeded, was actively refused, or timed out — the same signal `telnet` or `nc -zv` gives you, without needing shell access.

Open vs filtered vs closed

Open means something is actively listening and accepted the connection. Closed means the host responded but nothing is listening on that port (a TCP reset was returned). Filtered/timeout usually means a firewall is silently dropping the packets rather than rejecting them outright — this is the hardest state to diagnose without a check like this one, since your own connection attempt just seems to hang.

When you'd use this

Confirming a firewall rule actually took effect after a change, verifying a newly deployed service is reachable from the public internet before pointing DNS at it, or ruling out network-level blocking as the cause of a connection issue before digging into application logs.

Scope and limits

For safety, this tool only connects to publicly routable addresses — it won't attempt connections to private, loopback, or link-local ranges (including cloud metadata endpoints), since that could be used to probe internal infrastructure rather than test your own public-facing services.

Common ports and what they're used for

| Port | Service | |------|---------| | 22 | SSH (remote server access) | | 25 / 587 | SMTP (outgoing mail) | | 80 / 443 | HTTP / HTTPS (web traffic) | | 3306 | MySQL | | 3389 | RDP (Windows remote desktop) | | 5432 | PostgreSQL |

Does this check UDP too?

This tool tests TCP connectivity specifically, since a real TCP handshake gives an unambiguous open/closed/filtered result. UDP is connectionless by design, so a "port check" against it can only ever report whether a response came back, not a reliable open/closed state -- which is why most browser-based port checkers, including this one, focus on TCP.

Frequently asked questions

Open vs filtered vs closed — what's the difference?

Open means something is actively listening and accepted the connection. Closed means the host responded but nothing is listening on that port. Filtered/timeout usually means a firewall is silently dropping the packets.

Why does it reject some hosts I enter?

Private, loopback, link-local, and cloud-metadata address ranges are blocked on purpose — this tool is for testing your own public-facing services, not for probing internal networks.

Does this tool check UDP ports?

No, this checks TCP specifically -- TCP's handshake gives an unambiguous open/closed/filtered result, while UDP is connectionless and can't be reliably tested the same way from a browser-based tool.

Can I check ports on my home router or a private IP?

No -- this tool only connects to publicly routable addresses on purpose, so it can't be used to probe your own local network or internal infrastructure.

Why is a port shown as \'filtered\' instead of \'closed\'?

Closed means the host actively responded that nothing is listening. Filtered/timeout means no response came back at all -- almost always a firewall silently dropping the connection attempt rather than rejecting it.

How do I check if port 443 or 22 is open?

Enter the host name or IP, set the port number and press check. The result shows whether the TCP connection succeeded and how long it took.

Why is a port closed when my service is running?

Usually a firewall on the host or router blocks it, the service listens only on localhost, or the forwarding rule points to the wrong address.

Does the checker scan UDP ports?

No. UDP has no handshake, so an open port cannot be confirmed reliably from outside. The tool tests TCP only.

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