We present OSMAN (Open Source Metric for Measuring Arabic Narratives) - a novel open source Arabic readability metric and tool. The open source Java tool allows users to calculate readability for Arabic text (with and without diacritics). The tool provides methods to split the text into words and sentence, count syllables, Faseeh letters, hard and complex words in addition to adding diacritics (vocalise text). This makes the tool useful for researchers and educators working with Arabic text...