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-use-cases)<a href="https://agentmods.dev/skills/appsvortex/arness/arn-spark-use-cases"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-use-cases/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-use-cases"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-use-cases.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 | $0.00120 | $0.05981 |
| Opus 5.5 | $0.00048 | $0.02392 |
| Sonnet 5.5 | $0.00024 | $0.01196 |
| Haiku 4.5 | $0.00012 | $0.00598 |
Grade A, and why
arn-spark-use-cases 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 — 360 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Use Cases
Create structured use case documents in Cockburn fully-dressed format through a team-based conversational process, aided by the arn-spark-use-case-writer agent for drafting and revising, arn-spark-product-strategist for business relevance review, and arn-spark-ux-specialist for flow quality review (both are greenfield agents in this plugin -- if arn-spark-ux-specialist is unavailable, the skill proceeds with product strategist review only). This is a conversational skill that runs in normal conversation (NOT plan mode).
The primary artifacts are a use-cases/ directory at the project root containing individual use case files (UC-NNN-title.md) and a README.md index. Use cases are technology-agnostic behavioral descriptions that serve as the source of truth for what the application does from the actors' perspectives.
Use cases bridge the gap between the high-level product concept and the concrete artifacts consumed by downstream skills. They describe the WHAT (system behavior) not the HOW (implementation). Each use case specifies actors, preconditions, main success scenarios, alternate flows, postconditions, and business rules -- structured detail that the product concept alone does not provide.
For a richer review process where experts debate each other's findings (product strategist and UX specialist cross-review and respond to each other), use /arn-spark-use-cases-teams instead. The teams variant produces the same output format but through structured expert debate with mandatory per-round reports.
Prerequisites
The following artifacts inform the use cases. Check in order:
Determine the use cases output directory:
- Read the project's
CLAUDE.mdand check for a## Arnesssection - If found, extract the configured Use cases directory path — this is the source of truth
- 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 directory does not exist, create it
What ships with it
4 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 · 360 lines · 120 tokens per session scan A a2094f3e2202
arn-spark-use-cases is a skill published in the GitHub repository AppsVortex/arness (33 stars, last pushed today), licensed MIT. It adds 120 tokens to every session and 5,981 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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