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harness

harness is a skill for Claude Code from stone16/harness-engineering-skills. It costs 19 tokens per session (2,132 once invoked), scanned C, original, Apache-2.0.

A workflow for coordinating several fresh AI agents through planning, implementation, evaluation, and retrospective review. TDD, or test-driven development, means writing tests as part of the implementation process.

In plain words
What is it for?
Use it to turn an approved design into code, run checkpoint evaluations, perform end-to-end and full verification, create a pull request, and record lessons for future tasks.
Why use it?
It separates discovery, coding, checking, and learning so long tasks are less likely to drift away from the agreed requirements. Review checkpoints provide additional quality checks during execution.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: reads .claude/ paths; mentions CLAUDE.md; mentions subagents.

Part of the harness-engineering-skills plugin — 2 skills, 5 agents shipped together

not rated 31repo changed 1mo ago C scan 19 tokens original Apache-2.0

Good fit Use it to turn an approved design into code, run checkpoint evaluations, perform end-to-end and full verification, create a pull request, and record lessons for future tasks.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/stone16/harness-engineering-skills/harness
View source ↗ stone16/harness-engineering-skills
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add stone16/harness-engineering-skills --skill harness
Clone the repo
git clone --depth 1 https://github.com/stone16/harness-engineering-skills

Made for: Claude Code.

Or install harness-engineering-skills, the plugin that ships this one along with the rest of its 2 skills, 5 agents.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for harness

README.md
[![agentmods](https://agentmods.dev/badge/skills/stone16/harness-engineering-skills/harness/github.svg)](https://agentmods.dev/skills/stone16/harness-engineering-skills/harness)
Your own site
<a href="https://agentmods.dev/skills/stone16/harness-engineering-skills/harness"><img src="https://agentmods.dev/badge/skills/stone16/harness-engineering-skills/harness/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for harness

Your own site · 80×15
<a href="https://agentmods.dev/skills/stone16/harness-engineering-skills/harness"><img src="https://agentmods.dev/badge/skills/stone16/harness-engineering-skills/harness.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 19 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,132 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 2 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00019 $0.02132
Opus 5.5 $0.00008 $0.00853
Sonnet 5.5 $0.00004 $0.00426
Haiku 4.5 $0.00002 $0.00213

Measured 1mo ago against content hash fa569f7c62b4, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade C, and why

harness scanned grade C with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

The scan reads SKILL.md. This mod also ships 5 executable files (hooks/phase-guard.mjs, scripts/_cohort_spec.py, scripts/claude-agent-invoke.sh, …), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Reads agent configuration directoriesmediumAgent snooping

.claude/, .codex/, .gemini/ hold keys, settings and other credentials a mod has no legitimate need for.

Verify (review roles): `{ find ~/.claude/plugins -path '*/plugins/harness-engineering-skills/agents/harness-*.md' -type f 2>/dev/null; ls plugins/harness-engineering-skills/agents/harness-*.md 2>/dev/null; ls ~/.claude/a

Enumerates other installed skillsmediumAgent snooping

Other skills' SKILL.md files reveal prompts, capabilities and secrets that should be invisible to peers.

If not found, try `find ~/.claude/skills -path "*/harness/scripts/harness-engine.sh"` or `find ~/.codex/skills -path "*/harness/scripts/harness-engine.sh"` as fallback. In a checked-out repo, `plugins/harness-engineering
Origin

Copies of this mod

1 near-identical copy found in the catalogue:

  • harness — 89% identical, 41 lines differ
plugins/harness-engineering-skills/skills/harness/SKILL.md · 151 lines

How it starts

The opening of the file, as written. The whole thing — 151 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Harness — Multi-Agent Orchestration

Orchestrate complex tasks through Planning -> Generation -> Evaluation -> Retro. Fresh sub-agents per checkpoint prevent drift. Retro accumulates learning across tasks.

Protocol Loading

This skill splits into two protocol files to minimize context usage. Read the one matching your intent before proceeding.

Intent Trigger phrases Action
Planning "harness plan", "harness this task", "use harness", "harness spec" Read references/planning-protocol.md
Execution "harness continue", "harness execute ", "harness " Read references/execution-protocol.md

After loading the protocol, follow it completely. Do not proceed without reading the appropriate reference file.

Session 1 (Claude Code) → Brainstorm + Spec → Spec review with cross-model evaluator
    ↓ spec approved
Session 2 (Codex)       → Execute checkpoints → Evaluate → E2E → Full-verify → PR → Retro
    ↕ Claude CLI as review-loop peer (cross-model quality gate)
  • Session 1: Claude Code for interactive discovery — brainstorming + multi-turn Q&A to establish requirements. After the user approves the brainstormed design, spec drafting and the Spec Evaluator review loop run autonomously (agent-to-agent until consensus). See references/planning-protocol.md "Post-Brainstorming Autonomy".
  • Session 2: Codex for autonomous execution — implementation, evaluation, PR creation, retro. Claude CLI serves as cross-model reviewer via review-loop.
  • Both hosts support both phases. The above is the recommended flow, not a hard constraint.

Prerequisites

  1. superpowers plugin installed (Claude Code): Generator preloads TDD, verification, debugging skills
  2. Reviewer role definitions: harness-convention-scout.md, harness-spec-evaluator.md, harness-generator.md, harness-evaluator.md, harness-retro.md — ship with this plugin at plugins/harness-engineering-skills/agents/; user overrides may live at ~/.claude/agents/harness-*.md
  3. python3 on PATH (engine JSON operations)
  4. git repository initialized
  5. For Codex-hosted execution: claude CLI on PATH for sub-agent dispatch and review-loop

Read the full file on GitHub · 151 lines

Files

What ships with it

10 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago Changed · -9 lines · -111 tokens per session fa569f7c62b4
  2. 1mo ago First seen · 160 lines · 130 tokens per session scan C 4c5ba6587e98

Subscribe to this mod's changes

harness is a skill published in the GitHub repository stone16/harness-engineering-skills (31 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 19 tokens to every session and 2,132 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it C with 2 findings (reads agent configuration directories, enumerates other installed skills). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Building agentsClaude CodeCode reviewPlanningai-code-reviewclaudeclaude-code-plugincode-quality
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