Lean4Agent

This is the official repository for Lean4Agent: Formal Modeling and Verification for Agent Workflow and Trajectory. The Lean repository and experiment codes will be available soon.

Introduction

We introduce Lean4Agent, to the best of our knowledge, the first framework that uses Lean4 to model and verify agent behavior. Lean4Agent introduces FormalAgentLib, an extensible Lean4 library for formally modeling and verifying agent workflows’ semantic consistency under explicit assumptions, and enabling localization of execution-time failures revealed by trajectories. Building on FormalAgentLib, we further develop LeanEvolve, which applies the results in FormalAgentLib to revise workflows to enhance its capability. Extensive experiments on a hard problem subset of SWE-Bench-Verified and a subset of ELAIP-Bench across 5 leading LLMs indicate that the verification-passing workflows outperform the failing ones by an average of 11.94%, and LeanEvolve further improves SWE performance by 7.47% on average. Furthermore, Lean4Agent establishes a foundation for a new field of using expressive dependent-type FL to formally model and verify agent behavior.

Reference

@article{wang2026lean4agent,
  title={Lean4Agent: Formal Modeling and Verification for Agent Workflow and Trajectory},
  author={Wang, Ruida and Huang, Jerry and Wang, Pengcheng and Liu, Xuanqing and Kong, Luyang and Zhang, Tong},
  year={2026},
  note={Preprint}
}