We present the Vocabulometer, a reading assistant system designed to record the reading activity of a user with an eye tracker and to extract mutual information about the users and the read documents. The Vocabulometer stands as a web platform and can be used for analyzing the comprehension of the user, the comprehensibility of the document, predicting the difficult words, recommending document according to the reader's in order to increase his skills, etc. Since the last years, with the development of low-cost eye trackers, the technology is now accessible for many people, which will allow using data mining and machine learning algorithms for the mutual analysis of documents and readers.