The IP checker is designed to be used with the Ban IP Address/Range plugin to help mitigate issues around being locked out of your site.

The checker is  quite simple, it accepts the masks similar to the way the plugin does and features a target IP address. By default this is filled in with the detected IP address of the client. Upon entering the relevant data into the mask field and clicking "Check IP", two lines will appear below the heading.

The first possible line is "Matched indivdiual IP address". This means that an individual IP address from the mask field matched the target IP address. The second is "IP address was matched in range XXX.XXX.XXX.XXX/YY" where the range the address was detected in is displayed. When there are no matches, no lines are displayed.