XIDEK is an extensible interpreter development kit. It supports an interpreter and simple compiler development with a small but complete collection of reusable, extensible parsing and support modules. These modules implement standard expression and statement syntax, including control statements, symbol tables, abstract syntax trees, and simple bytecode interpreters. They can be used as a starting point for rapid development of language processors for script languages, "little languages", or domain-specific languages. Numerous documented examples show how to combine and extend the base modules into custom interpreters.