# Agent-as-Harness

The work introduces Harness-Zero: an agent-as-harness setup in which a harnessing agent reviews and minimally rewrites the student agent's proposals at its response boundary, translating guidance from an evolved harness (tools, middleware, skills, memory) into executable supervision inside the target harness's action space, followed by SFT on the reviewed trajectories; across SpreadsheetBench Verified, AppWorld, and USPTO retrosynthesis, training-free agent-as-harness averages 81.1% over six benchmark-model settings versus 78.1% for code-as-harness, while the distilled Qwen3.5-9B under a minimal target harness alone raises the macro average from 23.3% to 44.3%, surpassing the 41.7% of the base model with the evolved harness still attached, and recovers 82.

The work introduces Harness-Zero: an agent-as-harness setup in which a harnessing agent reviews and minimally rewrites the student agent's proposals at its response boundary, translating guidance from an evolved harness (tools, middleware, skills, memory) into executable supervision inside the target harness's action space, followed by SFT on the reviewed trajectories; across SpreadsheetBench Verified, AppWorld, and USPTO retrosynthesis, training-free agent-as-harness averages 81.1% over six benchmark-model settings versus 78.1% for code-as-harness, while the distilled Qwen3.5-9B under a minimal target harness alone raises the macro average from 23.3% to 44.3%, surpassing the 41.7% of the base model with the evolved harness still attached, and recovers 82.