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Paweł Huryn releases Mini Harness, a 1,200-line open-source coding harness

AIPaweł Huryn introduces Mini Harness, an open-source coding harness of about 1,200 lines of Python that he built as a Claude Code alternative. He says it includes /goal mode, permissions with auto mode, skills, MCP servers, and Anthropic's server-side compaction.

AIWhy it matters.

The post names the open-source harness's features and the Terminal-Bench 2.0 result, which helps readers compare agent harnesses on Claude Haiku 5.5.

Paweł HurynVerified on X
@PawelHuryn
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Everyone is discussing what a harness is. Nobody shows you how to build one. And everyone can.

So, I built my own Claude Code: https://github.com/phuryn/mini-harness

It's called Mini Harness: about 1,200 lines of Python.

Other minimal harnesses exist, but none has /goal mode, permissions + auto mode, skills and MCP servers. I wanted a fully working one to explain how a harness is built, down to Anthropic's server-side compaction.

Surprisingly, it became the top harness on Claude Haiku.

How it works: 🧵

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Paweł Huryn · x.comPublished · added here

Original title: Everyone is discussing what a harness is. Nobody shows you how to build one. And everyone can.

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AI agentsAI codingOpen-source ecosystemMCP & tool use