Your MySQL database is likely a critical component of your site and so this monitor will let you know if there is a problem. Rather than just test the default mysql port, it will in fact attempt to make a valid mysql connection. If your MySQL server does not respond appropriately then we know it is offline or unreachable. Note that MySQL login details are not required for this monitor to work. If you run your db on a non-standard port (in other words not on port 3306) then check out the MySQL - Port monitor.