We have developed and released HAGOROMO, a usage database of function words in Japanese, aiming to support Japanese language teachers, especially non-native teachers overseas, and learners at the intermediate and advanced levels. The system allows users to search function words, which are essential for Japanese language education/learning, and access authentic example sentences extracted from spoken and written language corpora. It is currently available in two forms̶as a web-based system (available at http://jreadability. net/hagoromo-dev), and as a downloadable Microsoft Excel data file. The number of headwords is 1,848; these were collected with reference to five pieces of reference literature including the previous JLPT test content specifications. The example sentences were extracted from four spoken language corpora including Meidai Dialogue Corpus, and four other written language corpora such as CASTEL/J. The levels of difficulty of the headwords were determined by the subjective judgments of five Japanese language teachers, each with experience of more than ten years.