json_generator

https://www.json-generator.com/

[
  '{{repeat(5, 7)}}',
  {
    _id: '{{objectId()}}',
    firstname: '{{firstName()}}',
    lastname: '{{surname()}}',
    contactinfo: {
        city: '{{city()}}',
      zipcode: '{{integer(100, 10000)}}',
        phone: '+1 {{phone()}}'
    }
  }
]