output.json

{
    "_meta": {
        "hostvars": {
            "my_host": {
                "my_variable": "foobar"
            }
        }
    }, 
    "all": {
        "children": [
            "my_group", 
            "ungrouped"
        ]
    }, 
    "my_group": {
        "hosts": [
            "my_host"
        ]
    }, 
    "ungrouped": {}
}