{
  "accounts/$accountId": {
    "fields": { "balance": "Int", "owner": "String!" },
    "tier": "durable",
    "rules": {
      "read": "@user.id != null",
      "create": "@user.id != null && @newData.owner == @user.id && @newData.balance == 0",
      "update": "@user.id != null && @data.owner == @user.id && @newData.owner == @data.owner && @newData.balance >= 0",
      "delete": "false"
    }
  }
}