Python 3.x – Json schema validator, how to validate if the key is not static

I am trying to validate this specific scheme:

{
"messages": [
        {
        "name": "test msg",
        "id": "0x100",
        "signals": {
                    "0": {"name": "Engine RPM", "bit_length": 16},
                    "16": {"name": "Gear", "bit_length": 3},
                    "19": {"name": "Battery Voltage", "bit_length": 5}
                   }
        }
    ]
}

I'm using the piton from jsonschema import Draft4Validator to validate this scheme … however, I'm not sure how to continue.

This is my current schema validation so far:

{
"$ schema": "https://json-schema.org/schema#",
"type": "object",
"properties":
{
"messages":
{
"type": "array",
"articles" :
{
"properties":
{
"first name" :
{
"type": "chain"
}
"I.D" :
{
"type": "chain"
}
"signs":
{
"type": "object"
}

"properties":
{


}
}
"necessary": ["name", "id", "signals"]
            }
}
}
}

The problem I'm facing is that I'm not sure how to deal with the objects that are in the "signals" key, since they start with a string and are NOT consistent ("0", "16", "19"). .. How could I validate this by making sure that the type is always a string, regardless of whether the string is consistent or not?

Thanks to all who respond in advance.