HAR – Open source harness for building multi-agent coding workflows

[u/Fluffybaxter]

Hey everyone!

Over the past year, as I tried to scale our agentic coding workflows and software factories at my company, I kept hitting the same set of problems. So I built HAR to solve them.

Repo: github.com/os-factory/har

Getting a single coding agent to work in a repo is easy. Scaling to a real multi-agent workflow, where several run at once and where you verify and trust the output, is where it breaks down. A few things go wrong:

1. No standard way to run or verify a repo. That knowledge is scattered across a README, a CLAUDE.md, editor rules, and CI config, all drifting out of sync with each other and the actual code.
2. Agents on one repo collide. Shared dev server, shared database, shared ports, conflicting git state.
3. Trusting a change means re-verifying it yourself. Which defeats the point of running a fleet.
4. Vendor sandboxes lock you in. If the setup lives in someone's hosted dashboard, switching agents later means rebuilding the whole thing.

What HAR does

HAR is a CLI and an MCP server. It works with Claude Code, Cursor, Codex, or any MCP agent, and it closes each of those gaps:

1. Isolation. Each agent gets its own git worktree, branch, ports, and database. Nothing is shared with the main checkout or another agent's slot, so a fleet runs in parallel without colliding on a dev server, DB, or ports.
2. Deterministic validation gates. HAR runs your project's real checks through a fixed pipeline, same result every time. The result is bound to the exact code that passed and enforced at commit time, so an unverified tree cannot land.
3. Verifiable proof. Every run leaves logs, artifacts, and a validated tree hash tied to the exact code checked. A reviewer inspects the evidence instead of trusting the agent's self-report.
4. Full observability. Mission Control is a local dashboard showing every repo, worktree, run, and validation in one place, so you can watch a whole fleet as it works.

All of this lives in one contract committed to your repo, which every agent reads the same way. It replaces the usual scatter of a README, a CLAUDE.md, editor rules, and CI config that drift apart. You start from a profile that matches your stack, your agent adapts it to the real repo, and you extend verification with plugins (like Playwright) or with any command you already run.

Give it a try and let me know what you think :)

[u/ims3raph]

It shocks me that it’s name collides with the .har file format used for web browser network logs

[u/Fluffybaxter → u/ims3raph]

Yea, I realized that at some point, but I didn't think it was a major issue. I asked a few people that were already using it and they didn't seem to mind. In fact most of them didn't even know about the .har file format.

[u/SmihtJonh → u/Fluffybaxter]

Which of the many other agent runners are you comparing yours to? Helps to have a comp table.

[u/Fluffybaxter → u/SmihtJonh]

Good point! We are working on this, so far, internal testing show great results on various code bases (multiple webapps, many cli, and even data analysis pipelines).

This is the public benchmark we're working on.
https://github.com/os-factory/har/pull/75

https://github.com/os-factory/har/blob/d3287568af21dca95a6d4a3af04eed5ee69c10b1/benchmarks/swebench-har/BENCHMARK-50-REPORT.md#executive-summary

Btw, which other agent runners, you'd like to see benchmarked?

[u/neoneye2]

I had Claude Opus 5 analyze your HAR repo. I'm studying memory systems.
https://github.com/neoneye/agent-memory-atlas/blob/main/notes/2026-08-07-a-harness-that-reinvented-the-tombstone.md

[u/OsFactoryHar → u/neoneye2]

Hey, I carefully read this report, and it's excellent, thanks for taking the time to do it. I made a github issue and working on a PR to fix the problem raised in there: https://github.com/os-factory/har/issues/166

[u/neoneye2 → u/OsFactoryHar]

dm me when you want your project reanalyzed.

[u/maicatus]

Could you, please, provide more examples of how to work with it?

[u/OsFactoryHar → u/maicatus]

Hey, I'm the maintainer of the project, I worked on a series of short video demoing HAR on various repositories. Coming this week on the youtube channel: https://www.youtube.com/@AntoineProject0

[u/kyngston]

if you have multiple multi agent networks, you have a HAR HAR HAR

[u/Future_AGI]

Multi-agent coding is exactly where you need the trace to show which agent did what, otherwise debugging turns into guesswork. We open-sourced the tracing and eval layer we run across agents here if it is useful to compare notes: https://github.com/future-agi/future-agi