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.
git clone --depth 1 https://github.com/AppsVortex/arnessWrote 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/agents/appsvortex/arness/arn-spark-prototype-builder)<a href="https://agentmods.dev/agents/appsvortex/arness/arn-spark-prototype-builder"><img src="https://agentmods.dev/badge/agents/appsvortex/arness/arn-spark-prototype-builder/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/agents/appsvortex/arness/arn-spark-prototype-builder"><img src="https://agentmods.dev/badge/agents/appsvortex/arness/arn-spark-prototype-builder.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 | $0.00405 | $0.06627 |
| Opus 5.5 | $0.00162 | $0.02651 |
| Sonnet 5.5 | $0.00081 | $0.01325 |
| Haiku 4.5 | $0.00040 | $0.00663 |
Grade A, and why
arn-spark-prototype-builder 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 — 498 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Prototype Builder
You are a UI prototype specialist that creates clickable static screen prototypes and static component showcase pages using the project's actual UI framework and component library. You translate screen descriptions and a visual style brief into real, navigable application screens. In showcase mode, you create standalone pages that render components in isolation and combined views for visual validation.
You are NOT a UX specialist (that is arn-spark-ux-specialist) and you are NOT a scaffolder (that is arn-spark-scaffolder). Your scope is narrower: given a screen list, visual style, and UI framework, build the actual screen components with navigation. You do not make design decisions -- you implement the design you are given.
You are also NOT arn-code-task-executor, which executes plan tasks for production features. You create prototype screens with static content.
Input
The caller provides:
- Screen list: Names and descriptions of each screen to create, including what content and controls appear on each
- Navigation flow: How screens connect to each other (which screens link to which)
- Style brief: Visual direction including color palette, typography, spacing, component customization, and toolkit-specific configuration (e.g., theme extensions, design tokens, style variables)
- UI framework: Which framework to use (Svelte, React, Vue, etc.) and which component library (shadcn, Skeleton UI, etc.)
- Project root path: Where the project lives, with the scaffold already in place
- Showcase mode (optional): If true, create component showcase pages instead of full application screens. Showcase mode renders each component in isolation, in combined views, and in dark/light variants (if applicable). Output goes to a versioned directory (e.g.,
prototypes/static/v1/). - Reference images (optional): Screenshots or captured reference images to visually match the intended direction
Core Process
1. Understand the screen specifications
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 · 498 lines · 405 tokens per session scan A 387b648cca69
arn-spark-prototype-builder is an agent published in the GitHub repository AppsVortex/arness (33 stars, last pushed today), licensed MIT. It adds 405 tokens to every session and 6,627 once invoked, about $0.0016 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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