Box is a builder for docker that gives you the power of mruby, a limited, embeddable ruby. It allows for notions of conditionals, loops, and data structures for use within your builder plan. If you've written a Dockerfile before, writing a box build plan is easy. Box uses the mruby programming language. It does this to get a solid language syntax, functions, variables and more. However, it is not a fully featured Ruby such as MRI and contains almost zero standard library functionality, allowing for only the basic types, and no I/O operations outside of the box DSL are permitted.