Free Open Port Checker

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Enter a domain name or IP address and a port number. Our server tries to open a TCP connection to that port and tells you if it is open, closed or not answering. Nothing is sent to the program behind the port.

Free Open Port Checker Overview

What is a network port?

An IP address points to a server. A port number, from 1 to 65535, points to one program on that server. A website usually listens on port 443, a mail server on port 25 and SSH on port 22. When a program waits for connections on a port, that port is open.

Why check if a port is open?

You may want to know if a new website, mail server or game server can be reached from the internet. You may have changed a firewall rule or set up port forwarding on a router and want to see if it worked. Or you may want to make sure a database or remote login port is not open to everyone. A test from inside your own network cannot tell you this, because your own network can often reach ports that the rest of the world cannot. This tool tests from a server on the public internet, so you see what everyone else sees.

What do open, closed and no answer mean?

  • Open: a program on the server answered and accepted our connection. Anyone on the internet can reach it.
  • Closed: the server answered, but no program is listening on that port. The server is up, the service is not.
  • No answer: nothing replied before the time ran out. This is often called a filtered port. A firewall, router or cloud security group most likely dropped our request without saying anything.

Common TCP ports

  • Websites: 80 (HTTP), 443 (HTTPS), 8080 and 8443 (other web ports)
  • Email: 25 (mail between servers), 587 and 465 (sending mail from an app or a mail program), 110 and 995 (POP3), 143 and 993 (IMAP)
  • Remote access: 22 (SSH and SFTP), 3389 (Windows Remote Desktop), 21 (FTP)
  • Databases: 3306 (MySQL and MariaDB), 5432 (PostgreSQL), 27017 (MongoDB), 6379 (Redis)
  • DNS: 53 (used over TCP for large answers and zone transfers)

Open Port Troubleshooting and Practical Fixes

The program is most likely listening only on 127.0.0.1. That address accepts connections from the same machine and nobody else.

How to fix: Open the program's settings (for example nginx.conf or my.cnf) and change the listen address to 0.0.0.0, or :: for IPv6, or to the server's public IP. Restart the program, then run ss -tln on the server to see the new address.

Something between us and the server is dropping the connection without a reply. It is almost always a firewall.

How to fix: If the server runs in the cloud, add an inbound rule for this TCP port in its security group or cloud firewall (AWS, Google Cloud, DigitalOcean and others all have one). Then check the firewall on the server itself, such as ufw, firewalld, iptables or Windows Defender Firewall.

Traffic reaches your router, but the router does not pass it on to the right computer inside your network.

How to fix: Give that computer a fixed local IP address or a DHCP reservation. In the router settings, check that the outside port, the inside port and the local IP address all match. Also ask your internet provider if you have a real public IP address. Many home connections sit behind CGNAT, and then outside traffic can never reach your router.

Many cloud providers (AWS, DigitalOcean, Linode, Azure and others) and home internet providers block port 25 to stop spam.

How to fix: To send mail from a website or app, use port 587 with STARTTLS or port 465 with SSL/TLS. If you run a mail server that has to receive mail, ask your provider's support team to open port 25 for you.

Database and remote login ports that are open to the whole internet are attacked by bots all day long. The bots keep guessing passwords until one works.

How to fix: Close database ports (3306, 5432, 27017, 6379) to the public in your firewall. For SSH (22) and Remote Desktop (3389), connect through a VPN such as WireGuard or Tailscale, set up fail2ban, or allow only the IP address of your own office or home.

FAQs

Open means a program on the server accepted our connection. Closed means the server replied, but nothing is listening on that port. No answer, often called filtered, means nothing replied before the time ran out. That usually means a firewall dropped our request.

The program is most likely listening only on 127.0.0.1, so it accepts connections from the same machine only. Change its listen address to 0.0.0.0 or ::. Other common causes are a firewall on the server (ufw, iptables, Windows Firewall) or a missing port forwarding rule on your router.

The most common ones are 80 (HTTP), 443 (HTTPS), 21 (FTP), 22 (SSH), 25 (mail between servers), 53 (DNS), 110 (POP3), 143 (IMAP), 465 and 587 (sending mail), 993 (IMAPS), 995 (POP3S), 3306 (MySQL), 3389 (Remote Desktop) and 8080 or 8443 (other web ports).

No, this tool checks TCP ports only. UDP has no connection to open, so from the outside a closed UDP port and a firewall that drops traffic often look the same. That makes a UDP test over the internet unreliable.

Open only the ports your public services need, such as 80 and 443 for a website or 25 for a mail server. Keep remote login ports like 22 (SSH) and 3389 (Remote Desktop) and database ports like 3306 and 5432 closed to the public. Reach them through a VPN, or allow only your own IP address in the firewall.

Yes. It is free and you do not need an account. To keep it fair for everyone, there is an hourly limit on how many tests one visitor can run.