The objective of this research is to present the design of a web application that predicts L2 text readability. The software is intended to assist ESL teachers in selecting texts written at a level of difficulty that corresponds with the target students' lexical competence. The ranges are obtained by statistical approach using distribution probability and an optimized version of the word frequency class algorithm, with the aid of WordNet and a lemmatised list for the British National Corpus. Additionally, the program is intended to facilitate the method of selection of specialised texts for teachers of ESP using proportionality and lists of specialised vocabulary. This web application is a free and open source software system which enables ESL/ESP teachers to carry out a comprehensive speed analysis without requiring knowledge of either computational linguistics or word frequency distributions and the underlying logarithmic proportionality.