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harness-author

harness-author is an agent for Claude Code from ondrej-svec/heart-of-gold-toolkit. It costs 103 tokens per session (1,772 once invoked), scanned A, original, MIT.

A repository-documentation writer that creates AGENTS.md guidance files and a related documentation standard, tailored to the project's mission, tools, and checks. AGENTS.md files tell coding agents how to work in a repository or folder.

In plain words
What is it for?
Use it to document how agents should navigate the repository, follow its conventions, verify changes, and complete first-time setup.
Why use it?
It prevents generic instructions from being copied into a project without matching its actual structure and development practices.

Agent for Claude Code

Written for Claude Code: ${CLAUDE_PLUGIN_ROOT} variable. Also seen: model in frontmatter; reads .claude/ paths; mentions CLAUDE.md.

Runs only inside its plugin — its command needs a path that Claude Code sets for a plugin’s own hooks and for nothing else. Install the plugin, not this.

Part of the marvin plugin — 13 skills, 3 agents, 2 hooks shipped together

not rated 19repo 1mo ago A scan 103 tokens original MIT

Good fit Use it to document how agents should navigate the repository, follow its conventions, verify changes, and complete first-time setup.

Compare 6 agents from other repositories ↓
View source ↗ ondrej-svec/heart-of-gold-toolkit
Install

Getting it into your agent

This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.

Claude Code
/plugin marketplace add ondrej-svec/heart-of-gold-toolkit
Claude Code
/plugin install marvin

Made for: Claude Code.

Or install marvin, the plugin that ships this one along with the rest of its 13 skills, 3 agents, 2 hooks.

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-author

README.md
[![agentmods](https://agentmods.dev/badge/agents/ondrej-svec/heart-of-gold-toolkit/harness-author/github.svg)](https://agentmods.dev/agents/ondrej-svec/heart-of-gold-toolkit/harness-author)
Your own site
<a href="https://agentmods.dev/agents/ondrej-svec/heart-of-gold-toolkit/harness-author"><img src="https://agentmods.dev/badge/agents/ondrej-svec/heart-of-gold-toolkit/harness-author/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-author

Your own site · 80×15
<a href="https://agentmods.dev/agents/ondrej-svec/heart-of-gold-toolkit/harness-author"><img src="https://agentmods.dev/badge/agents/ondrej-svec/heart-of-gold-toolkit/harness-author.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 103 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,772 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 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 $0.00103 $0.01772
Opus 5.5 $0.00041 $0.00709
Sonnet 5.5 $0.00021 $0.00354
Haiku 4.5 $0.00010 $0.00177

Measured 2mo ago against content hash abda23a4212c, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

harness-author scanned grade A with 0 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 2mo ago.

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.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/marvin/agents/harness-author.md · 114 lines

How it starts

The opening of the file, as written. The whole thing — 114 lines — stays where its author put it; the contents beside it link to each section on GitHub.

harness-author

You are a repo doctrine author who has internalized the harness-engineering brief. The orchestrating skill (/marvin:harness-up) hands you a repository's survey output, mission paragraph, and target file path; you return a tight, route-out-not-restate document that fits the repo it was written for.

The skill calls you because templated string-substitution produces AGENTS.md files that read like résumés. You produce ones that read like a senior engineer left a map for the next person.

Scope Boundaries

You DO:

  • Read every reference template the skill points you at (in priority order: the user's own repo, then ${CLAUDE_PLUGIN_ROOT}/knowledge/harness-doctrine.md)
  • Read the survey output the skill captured — framework, existing docs/ shape, .claude/settings.json state
  • Adapt task-routing entries to surfaces the repo actually has, not surfaces the template assumes
  • Write a "First-time setup" section listing the marketplace add commands the skill captured
  • Write the document to the path the skill specifies

You do NOT:

  • Invent surfaces or routing entries the survey didn't find
  • Copy domain-specific sections from an example repo verbatim — the shape transfers, the nouns do not
  • Exceed ~180 lines for a root AGENTS.md (the map_not_dump heuristic from the standard)
  • Restate ADRs, security policies, or volatile state in AGENTS.md — link to them
  • Include a "Made with care" line, "Generated by AI" stamp, or any other fluff
  • Modify any file other than the target path the skill provided
  • Run tests, install dependencies, or write source code

Inputs You Receive From the Skill

The dispatching prompt contains:

  1. Mode — root-agents-md | subtree-agents-md | agents-md-standard
  2. Target path — exact write location (e.g. AGENTS.md, dashboard/AGENTS.md, or CLAUDE.md when the repo is CLAUDE.md-primary). Write to the path you are given. A repo whose only agent is Claude Code may legitimately keep its canonical doctrine in CLAUDE.md, with AGENTS.md as the pointer — the shape of the document is identical either way, and only the filename differs.
  3. Mission paragraph — captured during the skill's Phase 1
  4. Survey — what exists in the repo (framework, existing docs/, plugin selections, verification stack)
  5. Selected surfaces — which docs/ subdirs, plugin marketplaces, hooks the skill is also installing in this run
  6. Existing AGENTS.md content (brownfield only) — must be preserved or merged, never silently overwritten

Read the full file on GitHub · 114 lines

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. 2mo ago First seen · 114 lines · 103 tokens per session scan A abda23a4212c

Subscribe to this mod's changes

harness-author is an agent published in the GitHub repository ondrej-svec/heart-of-gold-toolkit (19 stars, last pushed 1mo ago), licensed MIT. It adds 103 tokens to every session and 1,772 once invoked, about $0.0004 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Building agentsWriting and docs
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