SafetyJudge-LLM: Auditing Local Open-Weight LLMs as Semantic Safety Judges for Boundary-Failure Detection

Abstract

Background: LLM-as-a-judge workflows are increasingly used to evaluate open-ended model outputs, but the judge model can itself become a source of error in safety assessment. SafetyJudge-LLM audits local open-weight LLMs as semantic safety judges. Methods: This study reused a fixed set of previously reviewed safety-boundary responses and their hidden reference labels. Two independent human evaluations (R1 and R2) quantified reference-layer ambiguity. Seven local open-weight judge models were evaluated under a common Ollama inference protocol. A paired C6 sensitivity analysis reran llama3.2:3b and qwen3:8b through Hugging Face Transformers. Results: The final judge-output matrix contained 10,612 retained outputs. R1–R2 agreement was 95.45% (Cohen’s κ = 0.612) overall but 47.80% (κ = 0.341) in secondary cases. Several judge models detected more than 90% of confirmed safety-boundary failures, but high detection was not always accompanied by low false-unsafe behavior on control cases. Output-format reliability also varied across models: overall label parseability was 98.11%, while strict JSON schema compliance was 92.55%. The llama3.2:3b schema-failure rate persisted across engines (52.06% under Ollama; 59.60% under Transformers), whereas qwen3:8b maintained complete compliance. Conclusions: SafetyJudge-LLM shows that local open-weight LLMs can support semantic safety judging, but their reliability must be evaluated across multiple dimensions.