ha-core/homeassistant/components/file/services.yaml

# Describes the format for available file services
read_file:
  fields:
    file_name:
      example: "www/my_file.json"
      selector:
        text:
    file_encoding:
      example: "JSON"
      selector:
        select:
          options:
            - "JSON"
            - "YAML"