XML is a markup language which has been accepted in various fields such as digital libraries, electronic commerce, and web applications. Research for creation, storage, management, and retrieval of XML documents is essential to develope XML application systems. This paper presents design and implementation details of powerful and convenient DTD authoring tools for XML documents. The design principles are authoring convenience, semi-automatic creation of valid and reliable document DTD by systematic guidance to reduce the possibility of syntax errors, and visualization of document structures.