The Open Source Agent Framework That Is 44 Times Lighter Than Claude Code

OpenHarness: 44x lighter than Claude Code with 98% of features.

After Claude Code was open-sourced, the University of Hong Kong released an ultra-lightweight alternative: OpenHarness, a lightweight Agent Harness (Agent framework) implemented in Python. Its core code consists of just over 11,700 lines, yet it implements nearly 98% of the tool capabilities found in Claude Code, while being fully compatible with Anthropic’s skills system and the Claude-Code plugin ecosystem.

Project Overview

In simple terms, Agent Harness is the infrastructure layer that equips large language models with “hands, feet, eyes, and safety boundaries.” The model is responsible for thinking, while the Harness handles execution, memory, permission control, and multi-agent collaboration.