Gujin weishu kao 古今偽書考 "Research to text forgeries through all ages" is a commented bibliography of texts whose authenticity is doubted. The 2-juan long catalogue was compiled by Yao Jiheng 姚際恆 (1647-?), courtesy name Lifang 立方 or Shouyuan 首源, from Xiuning 休寧, Anhui, who also authored a discussion of Confucian Classics, Jiujing tonglun 九經通論, and the book Yongyanlu 庸言錄.
Before the Ming period 明 (1368-1644) many texts had been attributed to famous or even imaginary persons to boost the demand. Although there had been some scholars, particularly during the Song period 宋 (960-1279), that began doubting authorships or traditional dates of compilation of many texts, there was never a systematic and scholarly attempt at identifying forged texts.
Yao analysed nineteen commentaries to the Confucian Classics, thirteen histories and thirty-eight texts of so-called "Masters and Philosophers", and discussed the authenticity of a total of 91 books. Eight further texts were identified as authentic texts, but with forged parts, in six texts, the name of the author was fake, three texts the name whose author differed according to various sources, and four, whose author could not be identified.
For his research Yao Hengji made use of old bibliographies, like the bibliographic treatise Yiwen zhi 藝文志 in the official dynastic history Hanshu 漢書, the Jingji zhi 經籍志 of the history Suishu 隋書, or the Song-period catalogues Zhizhai shulu jieti 直齋書錄解題, Junzhai dushu zhi 郡齋讀書志, Song Lian's 宋濂 (1310-1381) Zhuzi bian 諸子辨 or Hu Yinglin's 胡應麟 (1551—1602) Sibu zheng'e 四部正訛.
Yao's book was later critically revised by Gu Shi 顧實 (c. 1887-1957, author of Chongding Gujin weishu kao 重考古今偽書考) and Huang Yunmei 黃雲眉 (1898-1977, Gujin weishu kao buzheng 古今偽書考補正).
Yao's text was the first book in which a larger corpus of texts was questioned, and therefore experienced a wide readership. It is to be found in the series Zhibuzuzhai congshu 知不足齋叢書, Jinshi'an congshu 晉石厂叢書, Shenshijizhai congshu 慎始基齋叢書, Bianwei congkan 辨偽叢刊, Juzhenban congshu 聚珍版叢書, Guji kaobian congkan 古籍考辨叢刊 and Congshu jicheng chubian 叢書集成初編.