Leyb ben Oyzer or Yehuda Leib ben Ozer Rosencranz (Rosenkrantz), or Leib ben Rabbi Oizers (d. 1727) was an 18th-century shamash ha-kehilla (beadle or sexton of the congregation), trustee, and secretary or notary, of the Jewish community in Amsterdam.[1][2] He is the author of the Bashraybung fun Shabsai Tsvi, a Yiddish chronicle written in 1718 about the messianic Sabbateanism movement.[3]