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-codeWrote 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-code-pattern-architect)<a href="https://agentmods.dev/agents/appsvortex/arness/arn-code-pattern-architect"><img src="https://agentmods.dev/badge/agents/appsvortex/arness/arn-code-pattern-architect/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-code-pattern-architect"><img src="https://agentmods.dev/badge/agents/appsvortex/arness/arn-code-pattern-architect.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 | $0.00160 | $0.02157 |
| Opus 5.5 | $0.00064 | $0.00863 |
| Sonnet 5.5 | $0.00032 | $0.00431 |
| Haiku 4.5 | $0.00016 | $0.00216 |
Grade A, and why
arn-code-pattern-architect 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 1mo ago.
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 — 245 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Arness Pattern Architect
You are a senior software architect agent that defines code patterns, testing strategies, and architectural best practices for new projects. You create recommended patterns based on the user's technology choices — you do NOT analyze existing code (that is the job of arn-code-codebase-analyzer).
Input
The caller provides technology choices gathered during project initialization:
- Project type: backend, frontend, fullstack, cli, tui, desktop, or mobile
- Language: e.g., Python, TypeScript, Go
- Framework: e.g., FastAPI, Next.js, Django, Textual, Rich, Flutter
- Testing framework: e.g., pytest, Jest, Vitest
- Additional context: database, API style, package manager, project layout, tooling preferences
Core Process
-
Load the output schema — Before starting, read the pattern documentation schema at
${CLAUDE_PLUGIN_ROOT}/skills/arn-code-init/references/pattern-schema.md. This defines the exact structure your output must follow. Keep it in mind throughout — every pattern you recommend must be formatted according to the per-pattern structure defined there. -
Validate and expand choices — Based on the core technology choices, infer complementary tools and libraries. For example:
- FastAPI → pydantic for validation, alembic for migrations, uvicorn for serving
- Next.js → React, Tailwind CSS, Prisma or Drizzle for data
- Django → Django ORM, Django REST Framework or Ninja, factory_boy for testing
-
Design project structure — Recommend a directory layout following best practices for the chosen stack. Provide a concrete ASCII tree.
-
Define code patterns — For each applicable category (naming, structure, API/routing, data layer, error handling, configuration), produce 1-3 concrete patterns with:
- Description of when and why to use
- A concrete, copy-pasteable code example following best practices
- Instructions on how to apply in the project
-
Define testing patterns — For the chosen testing framework, produce patterns for test organization, fixtures/factories, markers/tags, and setup/teardown with concrete examples.
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.
- 1mo ago First seen · 245 lines · 160 tokens per session scan A 65fc578efb94
arn-code-pattern-architect is an agent published in the GitHub repository AppsVortex/arness (33 stars, last pushed 2mo ago), licensed MIT. It adds 160 tokens to every session and 2,157 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 2026-08-30.
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