import csv


def sniff_csv_sep(file_path: str) -> str:
    """Determine and return the separator used in a given .csv file.

    Works by sniffing the first line of the given file.

    :param file_path:
        The file path of the .csv file.

    :return:
        Delimiter used in the given .csv file.

    """

    with open(file_path, 'r') as csv_file:
        dialect = csv.Sniffer().sniff(csv_file.readline())

    return dialect.delimiter