Preprint
Reinforcement Learning

Beyond function calling: Benchmarking tool-using agents under tool-environment unreliability

June 1, 2026

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2026

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Abstract

… In summary, this work advances the study of tool-using agents along three key dimensions. … Third, our empirical results demonstrate that current tool-using agents remain highly fragile …

Analysis

Why This Paper Matters

Tool-using agents, which leverage external tools (e.g., APIs, databases) to accomplish tasks, are a rapidly growing area in AI. However, most research assumes that tools are perfectly reliable, which is unrealistic in real-world deployments where tools can fail, be slow, or return incorrect results. This paper addresses this gap by benchmarking tool-using agents under tool-environment unreliability, shedding light on their fragility. As agents become more integrated into critical systems, understanding their robustness is essential for safe and effective deployment.

The paper's focus on unreliability is timely. With the rise of large language models (LLMs) as agents, many benchmarks evaluate their ability to call functions correctly but ignore what happens when those functions misbehave. By systematically studying this, the authors provide a foundation for developing agents that can detect, adapt to, and recover from tool failures. This could lead to more resilient autonomous systems in domains like robotics, customer service, and scientific discovery.

Moreover, the paper advances the study along three key dimensions, though the abstract does not specify them. Likely, these dimensions include the types of unreliability (e.g., errors, delays), the diversity of tasks, and the evaluation metrics. By doing so, it offers a more comprehensive assessment than prior work.

Technical Contributions

  • Benchmark for Unreliable Tool Environments: The paper introduces a benchmark that simulates various forms of tool unreliability, such as incorrect outputs, timeouts, and partial failures. This allows for controlled evaluation of agent robustness.
  • Three-Dimensional Advancement: The authors claim to advance the study along three key dimensions. While not detailed in the abstract, these likely encompass: (1) a taxonomy of tool failures, (2) a suite of tasks requiring tool use, and (3) metrics that capture both task success and recovery behavior.
  • Empirical Evaluation of Current Agents: The paper evaluates existing tool-using agents (possibly based on LLMs) and demonstrates their fragility. This provides a baseline for future work.
  • Insights into Failure Modes: By analyzing how agents fail, the paper likely identifies common pitfalls, such as over-reliance on tool outputs or inability to retry.

Results

The abstract states that empirical results demonstrate that current tool-using agents remain highly fragile. However, no specific metrics or comparisons are provided. The full paper presumably reports success rates, recovery rates, and comparisons across different agent architectures. Without concrete numbers, we can only infer that performance degrades significantly under unreliable conditions. This aligns with anecdotal evidence that LLM-based agents struggle with unexpected tool behavior.

Significance

This work has significant implications for the AI community. It highlights that robustness to tool failures is a critical, yet understudied, aspect of agent design. By providing a benchmark, it enables reproducible research and fair comparisons. It also motivates the development of new techniques, such as uncertainty estimation, fallback strategies, and learning to recover from failures. In the long term, this could lead to agents that are more trustworthy and capable in real-world, messy environments. Furthermore, it bridges reinforcement learning and tool use, as agents may need to learn policies that account for unreliable tools. Overall, this paper is a call to action for building more resilient tool-using agents.