The WCL development environment is really just a Lisp application that uses the Compiler, Common Lisp, and CLX libraries. GNU Emacs [#!emacs!#] and GDB also serve as useful development tools, although they are not required. When using Emacs, GDB mode is usually used to start an inferior GDB, which in turn starts an inferior WCL process. Unix profiling tools are also useful for analyzing performance.