Check if a port is open on any host
Our port checker tests whether a specific TCP port is reachable on a given IP address or domain. When you submit a check, our server attempts to establish a TCP connection to the target host on the specified port. If the connection succeeds, the port is reported as open. If the connection is refused, the port is closed. If no response is received within the timeout period, the port is reported as filtered, meaning a firewall is likely blocking the traffic.
Ports are essential to how networked applications communicate. Every internet service listens on one or more ports: web servers use port 80 (HTTP) and 443 (HTTPS), email servers use ports 25, 465, or 587 (SMTP), and SSH servers use port 22. Checking whether a port is open helps you verify that your server is correctly configured, that firewall rules are working as intended, and that services are accessible to users or other systems that need to reach them.
To use the tool, enter a hostname or IP address and the port number you want to check, then click the check button. You can also select from a list of common ports for quick testing. The result will tell you whether the port is open, closed, or filtered, along with the service typically associated with that port number.
A port is a numbered endpoint (0-65535) that identifies a specific process or service on a networked device. While an IP address directs traffic to the right machine, the port number directs it to the right application on that machine. Ports 0-1023 are “well-known” ports reserved for standard services (e.g., 80 for HTTP, 443 for HTTPS, 22 for SSH). Ports 1024-49151 are registered ports used by specific applications, and ports 49152-65535 are dynamic or private ports.
An “open” port means a service is actively listening and accepting connections on that port. A “closed” port means the host is reachable but no service is listening on that port, so the connection is actively refused. A “filtered” port means a firewall, router, or other network device is blocking the connection attempt, so no response is received at all. Filtered ports are neither confirmed open nor closed.
The most common ports include: 80 (HTTP web traffic), 443 (HTTPS encrypted web traffic), 22 (SSH secure shell), 21 (FTP file transfer), 25 (SMTP email sending), 53 (DNS domain name resolution), 3306 (MySQL database), 5432 (PostgreSQL database), 3389 (Windows Remote Desktop), and 8080 (alternative HTTP, often used for development servers or proxies).
The process depends on your operating system and firewall software. On Linux with UFW, use “sudo ufw allow [port]”. On Linux with iptables, use “sudo iptables -A INPUT -p tcp --dport [port] -j ACCEPT”. On Windows, open Windows Defender Firewall, go to Advanced Settings, and create a new Inbound Rule for the port. If you are behind a router, you may also need to configure port forwarding in your router’s admin panel.
Common reasons include: the service may be configured to listen only on localhost (127.0.0.1) instead of all interfaces (0.0.0.0), a firewall on the server may be blocking incoming connections, your ISP may be blocking the port, or if the server is behind a NAT router, port forwarding may not be configured. Check your service configuration, firewall rules, and router settings to resolve the issue.
