KillSwitch: a programming language built to confuse LLMs and coding agents

The author releases KillSwitch, an open-source esoteric stack-based language designed to be adversarial to LLMs and coding agents, with hidden lies in the spec and letter-counting rules in identifiers.

Claude Opus 5 scores best on the author's benchmark with 66.8, and the best open-weight model is MiMo-V2.6-Pro. The author says the simple tasks show performance but not clear proof that models understand the language.