# Harness Audit

Audit an agent's harness against the four rings: containment, guides, sensors...

- Repository: https://github.com/undefined-ui/second-brain-os (1169 stars)
- Category: AI and agents
- License: MIT
- Last updated: 2026-10-14
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add undefined-ui/second-brain-os --skill harness-audit -g -a claude-code -y`
Codex: `npx skills add undefined-ui/second-brain-os --skill harness-audit -g -a codex -y`
Cursor: `npx skills add undefined-ui/second-brain-os --skill harness-audit -g -a cursor -y`
Gemini CLI: `npx skills add undefined-ui/second-brain-os --skill harness-audit -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add undefined-ui/second-brain-os`

## Description

Audit an agent's harness against the four rings: containment, guides, sensors, permissions. Use when the user asks whether their agent setup is safe, wants a review of sandboxing / permissions / hooks / AGENTS.md guardrails, or asks what a bad session could break. Read-only: reports the blast radius and a hardening list, changes nothing. Do NOT use for context layout (context-audit) or cost routing (gate-check).

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Audit the four rings

Theory: [The four rings](https://secondbrainos.dev/#/read/course-4-harness/the-four-rings)
and [Harness practice](https://secondbrainos.dev/#/read/course-4-harness/harness-practice).
Build from the outside in: containment, guides, sensors, permissions. The
order matters because each ring must hold when every ring inside it fails, a guide can be ignored, a sensor can miss, an approval can be misclicked;
a wall does not care.

## Core rule

Report and rank; never harden anything yourself. The audit's one organising
question is the blast radius: describe the worst session possible under the
current setup and what it costs. If the user asks you to apply fixes
afterwards, that is a normal edit session, not this skill.

## Workflow

The rest: https://github.com/undefined-ui/second-brain-os/blob/HEAD/plugins/agents-course/skills/harness-audit/SKILL.md