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Role prompts fail in ways users choose: a fuzzing harness reached 89% coverage of adversarial behaviour where free-form prompting reached 39%

AspireAI community · arXiv (RoleFUZZER)
RoleFUZZER adapts coverage-guided fuzzing from software testing to search for user behaviours that break a model's stated role, crossing a grounded taxonomy of interaction types with the role under pressure and surfacing specification-grounded failure patterns. Across five role specifications and 15 campaigns it reaches at least 89% coverage of a 64-cell behaviour grid for every model and role tested, and at an equal conversation budget, dropping the grid and asking an LLM to invent targeting users free-form lowers coverage to 39-69% with fewer kinds of violations. The paper also reports that the same specification fails in opposite directions, with open-weight models overriding a player's safety signals while Claude Haiku 4.5 breaks character instead.
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