The Mozart development environment (MozartDev) is a set of APIs that can be used to build user-extensible compilers. The APIs offer persistent and transient representation for common program entities, parsers, transformation plug-ins and rendering engines. An example of application is Moka, a Java to Java compiler that parses Java and renders Java, while running arbitrary plug-ins on the program. Some example plug-ins have been written to perform tasks such as symbolic derivation of Java expressions, assertions, tracing of code, etc. The MozartDev environment is available from http://mozart-dev.sf.net under the GNU General Public License. -- Main.ChristopheDeDinechin - 14 Nov 2001