Zijian 字鑒 "Mirror of characters", also written 字鑑, is a book on Chinese characters written during the Yuan period 元 (1279-1368) by Li Wenzhong 李文仲, who hailed from Changzhou 長州 (modern Wuxian 吳縣, Jiangsu). It is known that his uncle Li Shiying 李世英 had written the book Leiyun 類韻, a dictionary arranged by rhyme.
The 5-juan long Zijian was planned as a supplement of the Leiyun. It was finished in 1321 and was written with the spirit that the shape of a character was its most fundamental spirit, its reading the second point, and the meaning was only the last point to be discussed. With the help of the large treasure of older character dictionaries, Li Wenzhong expanded the book of his uncle and created a book providing the "correct" shape of characters. These are arranged according to the system of the 206 Guangyun 廣韻 rhymes.
It helped to amend a lot of errors that had crept into the Confucian Classics and respective dictionaries, like the Wujing wenzi 五經文字 that had been compiled under the supervision of Zhang Can 張參 during the Tang period 唐 (618-907), or the Peixi 佩觽, an early Song-period product by Guo Zhongshu 郭忠恕 (d. 977).
Such typical errors were 槀 instead of 稾, or 隟 instead of 隙. Such errors could easily be amended, but a large amount of "wrong" characters had long become custom, like 墮 instead of 陊, or 隳 instead of 隓, and would continue to be used, as Li regretted.
The book was forgotten for a long time and was only rediscovered by Zhu Yizun 朱彝尊 (1629-1709) during the Kangxi reign-period 康熙 (1662-1722) of the Qing period 清 (1644-1911). A critical commentary on the Zijian, Jiaozhu Zijian 校注字鑒, was written by Fang Chenggui 方成珪 (1785-1850). Fang carefully analysed the ancient use of the Zijian characters and quoted, where it had been used in which sense, for instance, when the character 逄 was used instead of 逢, and when it was exchangeable.