We discuss tools that aid in the development, the assessment and the reengineering of language descriptions. The assessment tools give an indication as to what is wrong with an existing language description, and give hints towards correction. From a correct and complete language description, it is possible to generate a parser, a manual, and online documentation. The parser is geared towards reengineering purposes, but is also used to parse the examples that are contained in the documentation.The reengineered language description is a basic ingredient for a reengineering factory that can manipulate this language. We demonstrate our approach with a proprietary language for real time embedded software systems that is used in telecommunications industry. The described tool support can also be used to develop a language standard without syntax errors in the language description and its code examples.