At least some content in this article is derived from information featured in Harry Potter: Hogwarts Mystery. Spoilers will be present within the article.
These notebooks were a collection of journals that belonged to Jacob sometime between him being a student at Hogwarts School of Witchcraft and Wizardry, and being trapped in the Cursed Portrait Vault, and were used to chronicle progress reports pertaining to his search for the Cursed Vaults. These were often written in code to prevent others from reading them. According to Madam Rosmerta, the landlady of the Three Broomsticks Inn in Hogsmeade Village, Jacob would often spend his time at her establishment quietly writing in them.
- Harry Potter: Hogwarts Mystery (First appearance)