This simple Mac app scans entered japanese text and highlights its chinese characters (*kanji*) according to the school year in which they are taught in Japan. This tells you at a glance if your japanese text can be  easily read by a given audience.  The official list of which characters are taught in which year of elementary school is published by the Ministry of Education of Japan and can be downloaded online: http://www.mext.go.jp/a_menu/shotou/new-cs/youryou/syo/koku/001.htm