Open Port Check Tool

The open port checker tool allows you to check port status of your external IP address or any IP address you have entered and scan open ports on your connection. This tool is extremely useful to find out if your port forwarding is setup correct or if your server applications are blocked or not by a firewall. The open port checker tool can also be used as a port scanner to scan your network for ports that are commonly used such as HTTP (port 80). Some may be closed such as port 25 by default, are often blocked at the ISP level in order to prevent unwanted activities.

Screenshots from Chrome Web Store