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Harness of Harness

Multi-Day Autonomous Software Development with Continual Improvement

🗞️ News

• 🎉 2026-09-24 — HoH-lite, a lightweight, extensible implementation of HoH's core workflow, is available. Try it →
• 🎉 2026-09-23 — Focusboard, a Todo-list software, has reached a usable state. Watch demo →
• 🎉 2026-09-06 — Mournlight, a Vampire Survivors–style roguelite, has reached a playable state. Watch demo →
• 🎉 2026-09-02 — 🌐 Our project page is now live, featuring demo videos and project resources.
• 🎉 2026-09-02 — 📄 Our paper, Harness-of-Harness, is now available on arXiv.
• 🎉 2026-09-01 — Fusepoint, a single-player narrative first-person shooter, has reached 70+ loops. Watch demo →

Overview

We introduce Harness-of-Harness (HoH), a framework that equips coding agents with continual improvement capabilities for autonomous software development. HoH builds upon existing coding-agent harnesses and organizes development into iterative planning–coding–testing loops.

In a multi-day deployment with more than 70 iterations, HoH autonomously develops a first-person-shooter game, featuring a coherent storyline, fully implemented core mechanics, human-playable experience, polished visuals and integrated audio.

How It Works

Each iteration uses the same evolving project workspace and coordinates three stable roles:

• Project Planner — reads the public requirements and evidence from the previous iteration, then writes a prioritized development document. It does not modify the artifact.
• Developer — implements the current development document in the shared workspace while preserving functionality that has already been verified.
• QA Tester — executes and inspects the updated artifact against the requirements, recording evidence for verified behavior and unresolved gaps. It remains read-only.

The resulting artifact and evidence bundle become the starting state for the next iteration, allowing the system to improve loop by loop.

Demos

We will continue adding games, software, and demos across different genres. For each project, you can access the source repository and follow its development trajectory.

Project	Genre	Showcase	Download	Trajectory
Fusepoint	FPS
Mournlight	Roguelite
Focusboard	Productivity

Fusepoint

Mournlight

Focusboard

Code

🚀 HoH-lite is released! It is a lightweight, extensible implementation of HoH's core workflow. Get started, adapt it to your own benchmark or project, and build on it as you like.

🧰 The HoH system behind our demos builds on this foundation with more development and debugging tools, reusable skills, and project integrations.

💬 Ideas and contributions are welcome: open an issue or send a pull request.

Citation

@article{yan2026harness,
  title={Harness of Harness: Multi-Day Autonomous Software Development with Continual Improvement},
  author={Yan, Haoyang and Su, Min-Le and Zhang, Hangfan and Li, Zhanhao and Zhang, Chen and Zhang, Shao and Chen, Yang and Bai, Lei and Hu, Shuyue},
  journal={arXiv preprint},
  eprint={2609.01481},
  archivePrefix={arXiv},
  year={2026}
}

License

Original paper and demo materials in this repository are released under the MIT License. HoH-lite source under hoh-lite/ is released under Apache-2.0, with its own notices.

Contributors

We thank everyone who contributed to Harness of Harness and its case studies.

           

Contact

For questions, suggestions, or feedback, please feel free to contact us at:

yanhaoyang · suminle · zhanghangfan · lizhanhao · hushuyue @pjlab.org.cn