Malachi ben Jacob ha-Kohen (also known as the Yad Malachi) Montefoscoli (1695/1700? – 1772) was a renowned Talmudist, methodologist, and one of the greatest Kabbalists of the 18th century. He was a student of the famous kabbalist Rabbi Joseph Ergas, author of the original kabbalistic text known as Shomer Emunim. Born in Livorno sometime between 1695 and 1700, he passed on in the year 1772 and is considered the last of the great rabbinical authorities of Italy. Praised effusively by his contemporaries and quoted frequently by major halakhic authorities of the 18th and 19th centuries, he served as Rabbi of Livorno, Italy, and apparently lived to an old age. A decision by him, dated Nisan, 1732, and referring to a civil case at Rome, is included in the responsa of Rabbi Isaiah Bassani of Reggio (Todat Shelamim, No. 11, 1741). During the controversy between Jonathan Eybeschutz and Jacob Emden he sided with the former (letter of the rabbinate of Leghorn in "Luḥot 'Edut," p. 22).

He is most famous for his Yad Mal'aki (1766-7), a methodological work and compilation in three parts: part one contains an alphabetical list of all the rules and technical terms found in the Talmud, with explanations; part two deals with rules regarding the codifiers; part three deals with the rules relating to legal decisions, explaining certain general principles of legal responsa. Malachi wrote also a liturgical work, Shibḥe Todah (1744), containing prayers for the 22d of Shebaṭ, a fast-day instituted by the community of Leghorn. In addition to these, Malachi also wrote a Sefer Torah in his own hand which then became an authoritative reference for many details regarding the correct formation of various Hebrew letters.