The Datamuse API is used to integrate a word-finding query engine. It can be used in apps for programmatic access to Datamuse's websites, including OneLook, and Rhymezone. OneLook is a dictionary search application, and Rhymezone is used to find rhymes, and synonyms. It features autocomplete on text input fields, search relevancy ranking, assistive writing applications, and word games. Use the API in apps to query words that match constraints like meaning, spelling, sound, and vocabulary. This API returns data in JSON format.