장유는 조선 중후기 문신이자 문장가로서, 사상적으로는 성리학의 편협한 학문 풍토를 비판하고 불교와 도교, 양명학 등 다양한 사상에 관심을 가졌다. 『계곡만필』은 1635년(인조 13) 장유가 병중病中에 여러 가지 사항을 모아 편찬한 책으로, 자신의 학문과 글에 관한 설명, 평소에 보고 들은 한시·문장 등에 관한 고증과 비평 등 211항목이 실려 있다. 1643년(인조 21) 장유의 시문집인 『계곡선생집』과 함께 간행되었으며, 이 유물 역시 같은 시기에 간행된 판본으로 추정된다.

Jang Yu (pen name Gyegok) was a literary official and writer in the mid- to late Joseon Dynasty. He criticized the narrow-minded academic climate of neo-Confucianism and showed interest in various ideas such as Buddhism, Daoism, and Yangmingism. Gyegok manpil (Random Jottings of Jang Yu) was compiled by Jang in 1635 (the 13th year of King Injo’s reign) during a period of illness. It covers various subjects, containing 211 items, including explanations of his studies and writings, as well as proofs and criticisms of classical Chinese poetry and prose that he had read and heard. The compilation was published in 1643 (the 21st year of King Injo’s reign) alongside Gyegok seonsaengjip. This artifact is believed to be an edition published around the same time.