Natural-Language Agent Harnesses

arXiv cs.CL / 3/27/2026

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Key Points

  • The paper argues that agent performance depends heavily on “harness engineering,” but existing harness designs are often embedded in controller code and runtime-specific conventions that hinder transfer and scientific study.
  • It proposes Natural-Language Agent Harnesses (NLAHs) to express an agent harness’s high-level control logic as editable natural language.
  • It introduces an Intelligent Harness Runtime (IHR) that executes these harnesses via explicit contracts, durable artifacts, and lightweight adapters to improve portability.
  • The authors run controlled evaluations on coding and computer-use benchmarks, testing operational viability, module ablations, and migrating harness logic from code to text.

Abstract

Agent performance increasingly depends on \emph{harness engineering}, yet harness design is usually buried in controller code and runtime-specific conventions, making it hard to transfer, compare, and study as a scientific object. We ask whether the high-level control logic of an agent harness can instead be externalized as a portable executable artifact. We introduce \textbf{Natural-Language Agent Harnesses} (NLAHs), which express harness behavior in editable natural language, and \textbf{Intelligent Harness Runtime} (IHR), a shared runtime that executes these harnesses through explicit contracts, durable artifacts, and lightweight adapters. Across coding and computer-use benchmarks, we conduct controlled evaluations of operational viability, module ablation, and code-to-text harness migration.
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