schema.json

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "type": "array",
    "items": {
        "anyOf": [
            { "$ref": "#/$defs/target" },
            { "$ref": "#/$defs/group" }
        ]
    },
    "$defs": {
        "target": {
            "type": "object",
            "required": [
                "name",
                "hostname"
            ],
            "properties": {
                "name": {
                    "type": "string",
                    "pattern": "^[-_0-9a-zA-Z]+$"
                },
                "probe": { "type": "string" },
                "menu": { "type": "string" },
                "title": { "type": "string" },
                "hostname": { "type": "string" }
            },
            "additionalProperties": false
        },
        "group": {
            "type": "object",
            "required": [
                "name",
                "targets"
            ],
            "properties": {
                "name": {
                    "type": "string",
                    "pattern": "^[-_0-9a-zA-Z]+$"
                },
                "menu": { "type": "string" },
                "targets": {
                    "type": "array",
                    "items": { "$ref": "#/$defs/target" }
                }
            },
            "additionalProperties": false
        }
    }
}