AgentProcessBench: Diagnosing Step-Level Process Quality in Tool-Using Agents

TL;DR

AgentProcessBench is a new benchmark designed to evaluate step-level effectiveness of tool-using agents in realistic, open-ended scenarios, addressing the limitations of existing mathematical domain benchmarks.

Contribution

Introduces the first benchmark for step-level process quality in tool-using agents, with diverse trajectories, human annotations, and insights into model performance and challenges.

Findings

Weaker models tend to overestimate correctness due to early stopping.

Distinguishing neutral from erroneous actions remains difficult.

Process signals complement outcome supervision, improving scaling.

Abstract

While Large Language Models (LLMs) have evolved into tool-using agents, they remain brittle in long-horizon interactions. Unlike mathematical reasoning where errors are often rectifiable via backtracking, tool-use failures frequently induce irreversible side effects, making accurate step-level verification critical. However, existing process-level benchmarks are predominantly confined to closed-world mathematical domains, failing to capture the dynamic and open-ended nature of tool execution. To bridge this gap, we introduce AgentProcessBench, the first benchmark dedicated to evaluating step-level effectiveness in realistic, tool-augmented trajectories. The benchmark comprises 1,000 diverse trajectories and 8,509 human-labeled step annotations with 89.1% inter-annotator agreement. It features a ternary labeling scheme to capture exploration and an error propagation rule to reduce labeling ambiguity. Extensive experiments reveal key insights: (1) weaker policy models exhibit inflated ratios of correct steps due to early termination; (2) distinguishing neutral and erroneous actions remains a significant challenge for current models; and (3) process-derived signals provide complementary value to outcome supervision, significantly enhancing test-time scaling. We hope AgentProcessBench can foster future research in reward models and pave the way toward general agents. The code and data are available at https://github.com/RUCBM/AgentProcessBench.