schema.json

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "definitions": {
        "MyObject": {
            "properties": {
                "object": {
                    "$ref": "#/definitions/MySubObject"
                },
                "primitive": {
                    "$ref": "#/definitions/MyString"
                }
            },
            "required": [
                "primitive",
                "object"
            ],
            "additionalProperties": false,
            "type": "object"
        },
        "MyString": {
            "type": "string"
        },
        "MySubObject": {
            "properties": {
                "propA": {
                    "type": "number"
                },
                "propB": {
                    "type": "number"
                }
            },
            "required": [
                "propA",
                "propB"
            ],
            "additionalProperties": false,
            "type": "object"
        }
    },
    "$ref": "#/definitions/MyObject"
}