I’ve created a library that is like a pared-down version of Ghostwheel, but that works in a way that is more amenable for use as a type-like system for clj(s) development. It limits dependencies, and allows you finer control over how specs are applied to functions. Basically, you can co-locate declarations of expected args and return type with functions, then turn on/off an advisory or enforced (thrown exception) variant. Productions builds can choose not to suffer from any performance penalty or increase in build size. https://github.com/fulcrologic/guardrails/ NOTE: Alpha quality at this point. I’m sure I overlooked something…