Custom script can be created only by technical support by your request. Usually it is a file itself (installed at the dotcom-monitor server) with a set of rules (arguments)
JSON Object Example
{
    "File": "https_any.cs",
    "Arguments": "http://demopage.com parameter1 parameter2",
    "Device_Id": 8550,
    "Id": 17718,
    "Task_Type_Id": 39,
    "Name": "Custom Script",
    "Timeout": 0
}

Fields description 

Field Type Description

File

String

This field contains custom script filename. For more information, please contact technical support.

Example:
"File":"https_any.cs",

Arguments

String

This is custom script configuration field which contains unique arguments for each custom script. For more information, please contact technical support.

Example:
"Arguments": "http://demopage.com param1 param2"

Device_Id

Int32

READ ONLY Field.Unique device ID

Example:
"Device_Id": 8550

Id

Int32

READ ONLY Field.Unique task id

Example:
"Id": 17717

Task_Type_Id

Int32

Type of the task field. Please check Potential values for “Task_type_id” in appropriate table

Example:
"Task_Type_Id": 39

Name

String

Task name

Example:
"Name": "Custom Script"

Timeout

Int32

This field defines maximum time value (in mseconds) for task execution.

Example:
"Timeout": 0