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-spike)<a href="https://agentmods.dev/skills/appsvortex/arness/arn-spark-spike"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-spike/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-spike"><img src="https://agentmods.dev/badge/skills/appsvortex/arness/arn-spark-spike.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 | $0.00092 | $0.02643 |
| Opus 5.5 | $0.00037 | $0.01057 |
| Sonnet 5.5 | $0.00018 | $0.00529 |
| Haiku 4.5 | $0.00009 | $0.00264 |
Grade A, and why
arn-spark-spike 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 — 210 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Spike
Validate critical technical risks from the architecture vision through minimal proof-of-concept implementations, aided by the arn-spark-spike-runner agent for POC creation and execution. This is a conversational skill that runs in normal conversation (NOT plan mode). The primary artifacts are spike POC code in isolated directories and a spike results document.
This skill addresses the question: "Will the chosen technologies actually work for our use case?" It does not implement features or build the application -- it runs targeted experiments to validate or invalidate specific technical assumptions before committing to them.
Prerequisites
An architecture vision document should exist. Check in order:
- 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 and extract the "Known Risks & Mitigations" section.
If no architecture vision is found: Inform the user:
"No architecture vision document found. I can still run spikes if you describe the specific technical risks to validate. For a comprehensive risk assessment, run /arn-spark-arch-vision first."
If the user provides risks directly, proceed with those.
The project should ideally be scaffolded (via /arn-spark-scaffold) so the spike runner can leverage the existing project setup. If not scaffolded, spikes will need to set up their own dependencies, which the spike runner handles.
Determine the spike workspace:
- Read the project's
CLAUDE.mdand check for a## Arnesssection - If found, extract the configured Spikes 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
1 file 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 · 210 lines · 92 tokens per session scan A f4d82a6a06f4
arn-spark-spike is a skill published in the GitHub repository AppsVortex/arness (33 stars, last pushed today), licensed MIT. It adds 92 tokens to every session and 2,643 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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