```json
{
  "type": "object",
  "properties": {
    "name": {
      "type": "string"
    },
    "arguments": {
      "type": "object"
    }
  },
  "required": ["name", "arguments"]
}
```

This defines a tool call with:
- **`name`** — a required string identifying the function to call
- **`arguments`** — a required object holding the parameters (left open-ended; you can tighten it with `additionalProperties: false` and specific `properties` per tool)