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.
/plugin marketplace add AppsVortex/arness/plugin install arn-sparkWrote 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/appsvortex/arness/arn-spark-stress-premortem)<a href="https://agentmods.dev/skills/appsvortex/arness/arn-spark-stress-premortem"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-stress-premortem/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/appsvortex/arness/arn-spark-stress-premortem"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-stress-premortem.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 | $0.00118 | $0.02256 |
| Opus 5.5 | $0.00047 | $0.00902 |
| Sonnet 5.5 | $0.00024 | $0.00451 |
| Haiku 4.5 | $0.00012 | $0.00226 |
Grade A, and why
arn-spark-stress-premortem 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 today.
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 — 182 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Spark Stress Pre-Mortem
Stress-test a product concept using Gary Klein's pre-mortem methodology. Instead of asking "what could go wrong?" (which invites optimism bias), the pre-mortem declares that the product has already launched and failed, then investigates why.
The process works like this:
- Accept the premise: It is 12 months after launch. The product was shut down today.
- Investigate: A forensic investigator agent works backward from the failure to identify 3 distinct root causes -- a core experience flaw (A), a trust/security blind spot (B), and a target audience assumption error (C).
- Assess: Each root cause gets a causal chain, early warning signals, mitigation strategies, and a likelihood/severity rating.
- Prioritize: Root causes are mapped on a risk priority matrix to identify what needs immediate attention.
This technique surfaces failure modes that optimism obscures. The product concept is read but never modified -- all recommendations are captured in the pre-mortem report for later review.
Prerequisites
Configuration Check
- Read the project's
CLAUDE.mdand check for a## Arnesssection - If found, extract the configured Vision directory and Reports directory paths
- If no
## Arnesssection exists or Arness Spark fields are missing, inform the user: "Arness Spark is not configured for this project yet. Run/arn-brainstormingto get started — it will set everything up automatically." Do not proceed without it. - If the Reports directory does not exist, create it with
mkdir -p <reports-dir>/stress-tests/
Data Availability
| Artifact | Status | Location | Fallback |
|---|---|---|---|
| Product concept | REQUIRED | <vision-dir>/product-concept.md |
Cannot proceed without it -- suggest running /arn-spark-discover |
| Product pillars | ENRICHES | Product Pillars section of product concept | Investigation proceeds but pillar-as-evidence analysis is less targeted |
| Competitive landscape | ENRICHES | Competitive Landscape section of product concept | Root Cause C (market misread) is less grounded in competitive dynamics |
| Target personas | ENRICHES | Target Personas section of product concept | Root Cause A and C are less grounded in persona-specific failure scenarios |
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.
- today First seen · 182 lines · 118 tokens per session scan A 2404d3b0c466
arn-spark-stress-premortem is a skill published in the GitHub repository AppsVortex/arness (33 stars, last pushed today), licensed MIT. It adds 118 tokens to every session and 2,256 once invoked, about $0.0005 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 2026-10-25.
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