Here the cron regex :
(((\*)|(([0-9]|[0-5][0-9]))|(((\*|([0-9]|[0-5][0-9]))\/([0-9]|[0-5][0-9])))|(([0-9]|[0-5][0-9])(,([0-9]|[0-5][0-9]))*)|(([0-9]|[0-5][0-9])-([0-9]|[0-5][0-9])(\/([0-9]|[0-5][0-9]))?)) ((\*)|(([0-9]|[0-1][0-9]|2[0-3]))|(((\*|([0-9]|[0-1][0-9]|2[0-3]))\/([0-9]|[0-1][0-9]|2[0-3])))|(([0-9]|[0-1][0-9]|2[0-3])(,([0-9]|[0-1][0-9]|2[0-3]))*)|(([0-9]|[0-1][0-9]|2[0-3])-([0-9]|[0-1][0-9]|2[0-3])(\/([0-9]|[0-1][0-9]|2[0-3]))?)) ((\*)|(([0-9]|[0-1][0-9]|3[0-1]))|(((\*|([0-9]|[0-1][0-9]|3[0-1]))\/([0-9]|[0-1][0-9]|3[0-1])))|(([0-9]|[0-1][0-9]|3[0-1])(,([0-9]|[0-1][0-9]|3[0-1]))*)|(([0-9]|[0-1][0-9]|3[0-1])-([0-9]|[0-1][0-9]|3[0-1])(\/([0-9]|[0-1][0-9]|3[0-1]))?)) ((\*)|(([0-9]|0[0-9]|1[0-2]))|(((\*|([0-9]|0[0-9]|1[0-2]))\/([0-9]|0[0-9]|1[0-2])))|(([0-9]|0[0-9]|1[0-2])(,([0-9]|0[0-9]|1[0-2]))*)|(([0-9]|0[0-9]|1[0-2])-([0-9]|0[0-9]|1[0-2])(\/([0-9]|0[0-9]|1[0-2]))?)) ((\*)|(([0-7]))|(((\*|([0-7]))\/([0-7])))|(([0-7])(,([0-7]))*)|(([0-7])-([0-7])(\/([0-7]))?)))|(@reboot|@yearly|@annually|@