HAR

HAR is an open-source framework built by OS Factory that gives teams a structured way to run multiple coding agents concurrently on the same repository. Licensed under Apache 2.0 and available on GitHub, it works with Claude Code, Cursor, Codex, and any MCP-compatible agent without vendor lock-in. The project is sponsored by Kerno, a runtime code and security review tool for coding agents.

What It Is

HAR (the open harness for multi-agent coding workflows) is a CLI and MCP server that turns any repository into a fleet-ready environment. It introduces a machine-readable .har/ folder — a single contract that any supported coding agent reads the same way — replacing the scattered knowledge typically spread across READMEs, CLAUDE.md files, Cursor rules, and CI YAML. The harness handles isolation, deterministic verification, and evidence collection so that agents can focus on writing code and reviewers can trust the output.

How the Isolation Model Works

The core problem HAR addresses is that multiple agents working on the same repository collide: shared dev servers, shared databases, shared ports, and conflicting Git state. HAR solves this with a slot-per-agent model:

• Each agent gets its own worktree on a dedicated branch
• Each slot has dedicated ports and, where needed, its own database
• The main checkout stays untouched throughout any agent's session
• Slots can run concurrently without interfering with each other

The workflow moves through five stages: Discover → Isolate → Build → Verify → Hand off. After verification passes, the session tears down but the branch and evidence trail remain for reviewers.

Deterministic Verification and Evidence Trail

A key design goal of HAR is making agent output trustworthy without requiring a human to re-run the checks themselves. Every task runs the same deterministic verify pipeline and produces a consistent result. A full verification captures a validated tree hash tied to the exact code that was checked, along with logs and artifacts. The har env verify command runs the project's real checks — typechecks, unit tests, API health, lint, browser E2E, Docker builds — through the same pipeline every time.

The har env maintain command diffs the installed harness against current templates and flags drift before it causes a silent failure, addressing the common problem of hand-rolled scripts rotting as the stack changes.

Mission Control Dashboard

HAR ships with Mission Control, an open-source local dashboard that runs at localhost:3847. It provides:

• Live slots view — every active slot with its worktree, branch, and preview URL
• Run history — a timeline of every run with stage, trigger, duration, and status
• Traceable results — every result links back to the validation stages that ran and the exact Git tree they checked
• Artifact access — logs and artifacts accessible per run

Plugin Ecosystem and Stack Support

HAR uses profiles to adapt the harness to different project types: web apps (with per-slot ports and optional shared Docker infrastructure), CLI/library projects, and iOS apps (via Xcode and Swift with optional RocketSim flows). Plugins extend the harness with framework-specific stages:

• Playwright — adds a browser-e2e stage with frontend, API health, and accessibility smoke specs
• RocketSim — installs a rocketsim-flows runner for iOS simulator testing
• Custom stages can be registered for project-specific checks

Update: v0.47.0

The latest release is v0.47.0, published on August 6, 2026. The repository was created in late June 2026 and has been actively developed, with the last push recorded on August 8, 2026. The project is written in TypeScript and installable globally via npm (npm install -g @osfactory/har). A hosted cloud offering with centralized observability and shared Mission Control for organizations is listed as coming soon on the project homepage.