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-prototype-lock)<a href="https://agentmods.dev/skills/appsvortex/arness/arn-spark-prototype-lock"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-prototype-lock/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-prototype-lock"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-prototype-lock.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 | $0.00097 | $0.03230 |
| Opus 5.5 | $0.00039 | $0.01292 |
| Sonnet 5.5 | $0.00019 | $0.00646 |
| Haiku 4.5 | $0.00010 | $0.00323 |
Grade A, and why
arn-spark-prototype-lock 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 — 258 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Prototype Lock
Create a frozen, independently servable snapshot of the validated prototype before development code begins to modify shared source files. The primary artifacts are a frozen prototype copy, CLAUDE.md guardrail rules that prevent agents from modifying prototype files, an optional PreToolUse hook for enforcement, and a git tag marking the prototype completion point.
This skill addresses the problem: once development starts, production code overwrites prototype components because they share the same source files. The locked copy preserves the validated design reference for visual comparison and rollback.
Prerequisites
Read the project's CLAUDE.md for a ## Arness section. If no ## Arness section exists or Arness Spark fields are missing, inform the user: "Arness Spark is not configured for this project yet. Run /arn-brainstorming to get started — it will set everything up automatically." Do not proceed without it.
Extract:
- Prototypes directory (default:
.arness/prototypes) - Vision directory (default:
.arness/vision) - Git (yes/no)
- Platform (github/bitbucket/none)
Check for prototype validation evidence:
- Check for
[prototypes-dir]/clickable/final-report.md-- if found, read it. Extract the latest version number and judge verdict. - Check for
[prototypes-dir]/static/final-report.md-- same. - Check for
[prototypes-dir]/criteria.md
If no prototype validation evidence found: Inform the user: "No prototype validation results found. This skill works best after /arn-spark-clickable-prototype or /arn-spark-static-prototype has validated a prototype. You can still lock any existing prototype files. What prototype source should I preserve?"
If validation found but judge verdict was FAIL: Warn the user: "The latest prototype version (v[N]) received a FAIL verdict from the judge. Are you sure you want to lock this version, or would you prefer to run more validation cycles first?"
What ships with it
3 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 · 258 lines · 97 tokens per session scan A 49d256758ca6
arn-spark-prototype-lock is a skill published in the GitHub repository AppsVortex/arness (33 stars, last pushed today), licensed MIT. It adds 97 tokens to every session and 3,230 once invoked, about $0.0004 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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