check open ports,check for listening ports tool,domain/hostname/IP/URL

On this page you can check opened ports of domain/hostname/IP, it's the same as check listening of ports.
This tool trying to create port connection, connection timeout is 4 sec.
How to check available ports: just input destination in first field, and port (in listbox) or list of ports (in third field). After submit tools will scan ports.
A port scan helps the attacker find which ports are available (i.e., what service might be listing to a port). Essentially, a port scan consists of sending a message to each port, one at a time. The kind of response received indicates whether the port is used and can therefore be probed further for weakness.
To portsweep is to scan multiple hosts for a specific listening port. There are 65536 distinct and usable port numbers. Most services use a limited range of numbers. *This tool check ip open port too. You can scan port from list that is near fisrt input field too, but if third field is inputed - tools will use it, but not value from listbox.
Sometime if need to know some web server is dead or not, this tool can help you, because if www-80 is closed - it is when server is www inaccessible, else it's stay to recieve connections.

WIKI links :

what is port scaner, open port checker, how it's working