import json


def json_points(points):
    """
    Returns a list of points [(lat, lng)...] as a JSON formatted list of
    strings.

    >>> json_points([(1,2), (3,4)])
    '["1,2", "3,4"]'
    """
    return json.dumps(["{0},{1}".format(point[0], point[1]) for point in points])