The article presents the research of an Old Russian copy of Apostolos (Tolstovskii Apostolus,
National Library of Russia, Q.p.I.5) yet recently dated by the end of the 13th
– the 14th century. The codex stands out
among other Old Russian written sources having a unique structure. It represents a full-text version (the continuous text
type) of the Preslav recension. An online edition of the manuscript was accomplished at Kazan Federal University. This
machine-readable publication is accompanied by various search modules and indexes and located on the “Kazan digital
collection” page of the “Manuscript” portal. Recently, a hypothesis of the same provenance of this Apostolus and the
Onega Psalter (precisely dated by 1395) has emerged. Besides, it is assumed that both manuscripts were produced at a
Moscow scriptorium. The article critically examines these hypotheses describing the manuscripts’ history and
comparing their handwritings, orthographic systems, and decoration. The study presents an analysis of regional
characteristics of Tolstovskii Apostolus, which confirm its north-western origin and root relations with the book culture
of the 14th century. The analysis of the linguistic parameters of both codices was undertaken for the first time