Along with religious poet Eleazar ha-Kalir (Eleazar ben Kalir), Yannai was a famous author of sophisticated prayer-poems (piyyutim) intended for insertion at certain points in the Jewish synagogue liturgy. Little is known of his life other than that he lived in Palestine as a rabbi and wrote Jewish liturgical poetry. Yannai is the first synagogue poet, possibly following earlier Samaritan and Christian liturgical practice, to sign his compositions acrostically. He wrote a cycle of some 167 poetic insertions for the Amidah (“standing before God”), the main statutory prayer of the synagogue. Entitled Mahazor Yannai (sixth century c.e.; English translation, 1919), these poems were designed to connect the most important prayer of the Sabbath service with the content of the weekly Torah reading and its Midrashic commentaries. This followed a triennial cyclical pattern used in the Byzantine period that lasted only until the Babylonian Torah-reading cycle replaced it, thus effectively eliminating these liturgical prayer-poems from common use and the need for creating them.
The Mahazor Yannai and certain of Yannai’s compositions for other occasions were highly prized and were copied for centuries for use in the synagogue liturgy. Many copies turned up in the Cairo Genizah. The literary heritage of Yannai constitutes a major source for knowledge of the literature, beliefs, and religious concepts of the sixth century synagogue.