ResearchResearch paperMultimodal Models · Large Language Models · Speech & Audio1 source · Oct 12, 2026

ToolHACE: A Dataset for Detecting Hallucinations in Tool-Based LLM Responses

To address this gap, we introduce ToolHACE, a span-level benchmark for hallucination detection in tool-augmented LLM responses, covering five fine-grained hallucination categories.

Key points

  • Tool-augmented language models ground their responses in external tool outputs, improving reliability beyond parametric knowledge alone.
  • Existing hallucination benchmarks for tool-augmented dialogue primarily focus on the tool-calling stage, evaluating whether the correct tool and arguments are selected, while overlooking errors that arise during post-tool response generation.
  • Through extensive experiments with modern hallucination detectors, we show that post-tool-call hallucinations are widespread and remain challenging to detect.
  • Our results further demonstrate that effective detection requires training on specialized tool-augmented corpora, while transfer from tool-agnostic hallucination datasets performs poorly in this setting.

Sources (1)

  • [1]ToolHACE: A Dataset for Detecting Hallucinations in Tool-Based LLM Responses
    arXiv (AI, ML, NLP, CV, robotics, multi-agent) · Oct 12, 05:15 PM
    To address this gap, we introduce ToolHACE, a span-level benchmark for hallucination detection in tool-augmented LLM responses, covering five fine-grained hallucination categories.
    Tool-augmented language models ground their responses in external tool outputs, improving reliability beyond parametric knowledge alone.

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