How do I check if a port is open?

Enter the hostname or IP address and the port number, then start the check. The tool attempts to connect to that port and reports whether it is reachable.

Which ports can I check?

You can check standard TCP ports and custom port numbers, including common ports such as 80 for HTTP, 443 for HTTPS, 22 for SSH, and 21 for FTP.

Can a port checker tell me if my firewall is blocking a port?

A port checker can help identify whether a port is reachable from outside your network. A failed connection can also be caused by a closed port, router configuration, or a service that is not running.

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Port Checker Online Free

Check if a specific TCP port is open or closed on any server or domain. Test individual ports or scan common services at once.

All Network and Web Tools

Host or IP address

Port

Common ports:

Open The service accepted a connection.

Closed The host answered and refused. Nothing is listening.

Filtered No answer at all, which usually means a firewall dropped the packet.

Needs review Open, but this is a port that rarely belongs on the public internet.

Why this runs on our server. A web page has no access to raw TCP. Browsers also refuse to connect to ports like 22, 25 and 3389 outright, and they deliberately hide the difference between refused, blocked and slow. That is a security rule: without it, any website you visited could scan the network you are sitting on. So the check happens server side, where a real connection can be attempted and the real result reported.

Scan responsibly. Only scan hosts you own or have permission to test. Private and reserved address ranges are blocked. Unsolicited scanning of other people's infrastructure is, depending on where you are, against the terms of service of most hosts and in some places against the law.

About This Tool

Why this port checker runs on our server, not in your browser

A real port scanner opens a raw TCP socket and attempts the three way handshake described in RFC 9293, the current TCP specification: a SYN packet out, a SYN-ACK back if the port is listening, or a RST if it is closed, or nothing at all if a firewall is silently dropping the traffic. Browsers have no API for raw sockets. JavaScript running on a web page cannot open one, cannot send a bare SYN, and cannot read the resulting flags, and browsers refuse ports such as 22, 25 and 3389 outright. So this tool does not guess from your browser. It asks our server to make a real TCP connection and report what happened.

How the check actually works

Step 1 Address check The host name or IPv4 address is cleaned up and sent to our server with the port numbers. The server resolves the name and refuses private and reserved ranges, so it cannot be used to probe anyone's internal network.

Step 2 TCP connect For each port the server attempts a normal TCP connection, the same three way handshake any client makes, and waits up to about 3 seconds for an answer.

Step 3 Reading the outcome If the handshake completes, the port is open. If the host answers with a reset, the port is closed. If nothing comes back before the timeout, the port is filtered, which usually means a firewall dropped the packet.

Step 4 Common ports scan Scan common ports checks 19 well known ports, five at a time: FTP, SSH, SMTP, DNS, HTTP, POP3, IMAP, HTTPS, SMTPS, mail submission, IMAPS, POP3S, MySQL, RDP, PostgreSQL, Redis, 8080, 8443 and MongoDB. Results can be copied or downloaded as CSV.

Open means the port accepts connections, not that the service is healthy. The check stops after the handshake. It does not log in, send data or identify the software that is listening. It tests TCP only, so UDP services such as WireGuard or most game servers cannot be checked this way.

Reading the result honestly

Reported state	What it actually confirms
Open	Our server completed a TCP handshake with that host and port
Closed	The host answered and refused the connection, so nothing is listening there
Filtered	No answer within about 3 seconds, usually a firewall silently dropping the packet
Needs review	Open, on a port such as a database, RDP or Redis that rarely belongs on the public internet

Real TCP connect, not a browser guess About 3 second timeout per port 19 common ports on batch scan

RFC 9293 defines the TCP three way handshake our server performs for each port.
IANA's service name and port number registry is the authoritative list behind the common port labels shown in results.
nmap's port scanning basics guide explains true SYN, connect, and filtered scan states in detail.

When a port matters

A quick sanity check that a web server is actually reachable on 80 and 443 before digging further, confirming a firewall change took effect from outside your own network, checking whether a self hosted service is exposed to the internet when it should only be reachable locally, and spotting an obviously misconfigured server before running a heavier, more precise scan with dedicated tooling.

Common Questions

FAQ: Port Checker Online Free

A port checker tests whether a specific network port on a server or IP address is reachable from the internet. It can help determine whether a service such as HTTP, HTTPS, SSH, or FTP is accessible.

Enter the hostname or IP address and the port number you want to test, then start the check. The tool attempts to connect to that port and reports whether it is reachable.

An open port means a service is accepting connections on that port. A closed port means the host is reachable but no service is accepting connections there. A filtered or unreachable result can indicate a firewall or network rule blocking the connection.

You can check standard TCP ports as well as custom port numbers, depending on what your server or network service uses. Common examples include port 80 for HTTP, 443 for HTTPS, 22 for SSH, and 21 for FTP.

Yes, a port checker can help identify whether a port is reachable from outside your network. If the connection fails, the cause could be a firewall, router configuration, closed port, or a service that is not running, so the result should be used as a connectivity check rather than a definitive firewall diagnosis.

From the blog