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-dev-setup)<a href="https://agentmods.dev/skills/appsvortex/arness/arn-spark-dev-setup"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-dev-setup/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-dev-setup"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-dev-setup.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 | $0.00152 | $0.03847 |
| Opus 5.5 | $0.00061 | $0.01539 |
| Sonnet 5.5 | $0.00030 | $0.00769 |
| Haiku 4.5 | $0.00015 | $0.00385 |
Grade A, and why
arn-spark-dev-setup 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 — 367 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Dev Setup
Define or follow a standardized development environment through guided conversation, aided by the arn-spark-dev-env-builder agent for file generation and optionally the arn-spark-tech-evaluator agent for environment comparisons. This is a conversational skill that runs in normal conversation (NOT plan mode). The primary artifacts are development environment infrastructure files (setup scripts, container configs, CI workflows, toolchain pins) and a dev-setup document.
This skill covers the development environment: how developers get the project running on their machines, how CI builds and tests, and how toolchain versions are pinned for reproducibility. It does not create project source code (that is /arn-spark-scaffold) or validate technical risks (that is /arn-spark-spike).
This skill operates in two modes:
- Define mode: An architect or project lead defines the standard development environment. The skill asks questions, generates infrastructure files, writes a dev-setup document, and stores configuration in CLAUDE.md.
- Onboard mode: A developer joining the project follows the existing standard. The skill reads the configuration from CLAUDE.md, presents the setup steps, and guides the developer through the process.
Prerequisites
The following artifacts inform the development environment. Check in order:
Architecture vision (recommended):
- Read the project's
CLAUDE.mdfor a## Arnesssection. If found, check the configured Vision directory forarchitecture-vision.md - If no
## Arnesssection found, check.arness/vision/architecture-vision.mdat the project root
If an architecture vision is found: Read it for stack decisions (framework, languages, platform targets, system dependencies).
If no architecture vision is found: Ask the user to describe their stack: "No architecture vision found. Describe your technology stack and target platforms so I can configure the development environment."
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 · 367 lines · 152 tokens per session scan A ec99ebfc1eab
arn-spark-dev-setup is a skill published in the GitHub repository AppsVortex/arness (33 stars, last pushed today), licensed MIT. It adds 152 tokens to every session and 3,847 once invoked, about $0.0006 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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