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.
npx skills add fiveonecode/agent-skills --skill harness-engineeringgit clone --depth 1 https://github.com/fiveonecode/agent-skillsWrote 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.
[](https://agentmods.dev/skills/fiveonecode/agent-skills/harness-engineering)<a href="https://agentmods.dev/skills/fiveonecode/agent-skills/harness-engineering"><img src="https://agentmods.dev/badge/skills/fiveonecode/agent-skills/harness-engineering/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.
<a href="https://agentmods.dev/skills/fiveonecode/agent-skills/harness-engineering"><img src="https://agentmods.dev/badge/skills/fiveonecode/agent-skills/harness-engineering.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00067 | $0.00924 |
| Opus 5.5 | $0.00027 | $0.00370 |
| Sonnet 5.5 | $0.00013 | $0.00185 |
| Haiku 4.5 | $0.00007 | $0.00092 |
Grade A, and why
harness-engineering 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 98 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Harness Engineering
Overview
Use this skill to translate harness engineering principles into concrete repository changes that improve agent speed, correctness, and maintainability.
Workflow
1) Assess the current harness
- Inspect
AGENTS.md, contributor docs, CI workflows, and repo scripts. - Map the actual path from prompt to merged change.
- List concrete failure modes: ambiguous instructions, repeated mistakes, slow reviews, merge conflicts, stale docs, or noisy CI.
2) Define operating boundaries
- Separate decisions by layer:
- Human layer: architecture, taste, policy, and final risk acceptance.
- Agent layer: implementation, refactors, test updates, and routine maintenance.
- Define non-negotiable constraints before coding starts:
- Required tests and linters.
- Directory ownership and file-scoping rules.
- Branch, PR, and commit conventions.
3) Make the repository the system of record
- Encode process in files, not tribal knowledge.
- Prefer deterministic entry points:
- Single source for setup.
- Canonical command wrappers (
make,just, or scripts). - Stable templates for PRs, issues, and specs.
- Remove conflicting guidance and duplicate docs.
4) Increase agent legibility
- Prefer one clear pattern over many equivalent ones.
- Standardize naming, folder layouts, and module boundaries.
- Add concise examples for fragile tasks.
- Eliminate hidden behavior and implicit coupling.
5) Add mechanical guardrails
- Enforce checks automatically:
- Fast local checks for iteration.
- CI gates for merge readiness.
- Static analysis for known failure classes.
- Fail with actionable messages that point to exact fixes.
- Keep checks strict enough to prevent regressions, but fast enough for daily use.
- For any verifier or generated QA artifact, check verifier integrity before trusting a pass result.
6) Optimize merge throughput
- Encourage smaller, composable changes instead of large batches.
- Isolate independent work streams to reduce collisions.
- Define explicit integration rules for overlapping files.
- Prefer rapid merge and follow-up fixes over long-lived divergence.
What ships with it
2 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.
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.
- 1mo ago First seen · 98 lines · 67 tokens per session scan A 7ce618a09328
harness-engineering is a skill published in the GitHub repository fiveonecode/agent-skills (19 stars, last pushed 1mo ago), licensed MIT. It adds 67 tokens to every session and 924 once invoked, about $0.0003 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.
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