Debugging is a laborious, manual activity that often involves the repetition of common operations. Ideally, users should be able to describe these repetitious operations as little programs. Debuggers should therefore be programmable, or scriptable. The operating environment of these scripts, however, imposes interesting design challenges on the programming language in which these scripts will be written.This paper presents our design of a language for scripting debuggers. The language offers powerful primitives that can precisely and concisely capture many important debugging and comprehension metaphors. The paper also describes a debugger for the Java language built in accordance with these principles. We have implemented this debugger to run alongside the Java Virtual Machine. The paper includes concrete examples of applying this debugger to programs.