harness-stack

harness-stack

An agent-first development harness — a curated stack of tools that keep an AI coding agent building stably, durably, and at high quality.

Philosophy: Humans provide direction, agents execute.

What is harness-stack?

harness-stack is the harness around the agent: a collection of Skills, Commands, and Subagents that an AI coding agent reaches for while doing real engineering work. Each tool encodes one process a senior engineer would follow — defining specs, designing, debugging, reviewing, shipping — so the work comes out consistent and verifiable instead of improvised.

Everything is addressed through the harness-stack: plugin namespace, and everything lives in the repo: an agent that can't read it doesn't know it. There is no out-of-band CLI — every operation is a Skill or a Subagent.

FDD — the core

Feature-Driven Development (/harness-stack:fdd) is the heart of the stack. It is a contract-first, multi-agent loop that turns a goal into shipped, verified code. Three roles, each running in a fresh context so judgment never blurs:

• Coordinator — fdd orchestrates the flow; fdd-execution drives the serial build loop, dispatching one feature at a time and gating each handoff.
• Implementer — the implementer subagent builds exactly one bounded feature (test-first when required) and reports a structured handoff.
• Validator — a cost-increasing pipeline (fdd-validate) that probes the work against the contract: static gate (scrutiny-validator: test / lint / type-check + scrutiny) → review (code-reviewer: five axes, plus security-auditor when warranted) → behavioral user-test (user-test-validator).

The glue is the validation contract (fdd-validation-contract): the definition of done written as testable, user-observable assertions before code is written. The coordinator/implementer/validator triad checks every milestone against that contract — that's what keeps the program continuously converging on the goal at high quality rather than drifting.

Tool	Role in FDD
/harness-stack:fdd	Orchestrator — runs the 3-step main flow (the only one you invoke directly)
/harness-stack:fdd-planning	Step 1 — capture the plan and break it into features
/harness-stack:fdd-validation-contract	Step 1 — write the definition-of-done assertions
/harness-stack:fdd-execution	Step 2 — the serial per-feature build loop
/harness-stack:fdd-validate	Step 3 — milestone & final gates (static → review → user-test)
/harness-stack:tdd	Test-first development, used inside an implementer's task

Use FDD for any non-trivial change — one that touches multiple files, has several acceptance criteria, or spans more than one feature.

Tools

Individual tools, each doing one job. Mix and match — only FDD is a coordinated group.

Tool	What it does
/harness-stack:define-product	Define the product — what it is and why (product-spec.md)
/harness-stack:define-architecture	Define the system's structural map (architecture.md)
/harness-stack:define-api-spec	Define the authoritative API contract (api-spec.md)
/harness-stack:define-frontend-spec	Define frontend engineering conventions & quality bars
/harness-stack:define-ui-spec	Define the UI design system (DESIGN.md)
/harness-stack:design	Write a standalone technical design doc before building
/harness-stack:debug	Systematic root-cause debugging and recovery
/harness-stack:review-request	Dispatch fresh-context reviewers (code / security / tests)
/harness-stack:review-receive	Handle reviewer feedback with rigor, not theater
/harness-stack:security	Security audit and hardening
/harness-stack:debate	Multi-round debate among heterogeneous LLM agents
/harness-stack:decide	One-shot parallel decision support with synthesis
/harness-stack:changelog	Create and maintain CHANGELOG.md
/harness-stack:git	Disciplined git workflow and versioning
/harness-stack:pr	Open a PR and drive it to a clean merge
/harness-stack:ship	Pre-launch checklist, monitoring, rollback plan
/harness-stack:docs-init	One-time scaffold of a project's docs structure
/harness-stack:env-init	Per-worktree isolated runtime environment
/harness-stack:skill-create	Create a new harness-stack skill
/harness-stack:feedback	Reflect on a session and file an upstream issue

Commands

Thin slash-command entry points that delegate into the skills above — the substance lives in the skill.