arn-code-architect

A coding agent that designs how a proposed feature should fit into an existing codebase. It studies the project’s documented patterns and turns the feature idea into a concrete technical approach.

In plain words
What is it for?
Use it to plan the architecture of a specific feature, compare implementation options, and answer focused design questions about an existing project.
Why use it?
It helps answer implementation questions before coding begins, such as which existing components to extend and how the project’s conventions affect the design.

Agent

Install

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.

agentmods
npx agentmods add agents/appsvortex/arness/arn-code-architect
Clone the repo
git clone --depth 1 https://github.com/AppsVortex/arness
Per session 146 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,508 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00146 $0.01508
Opus 5 $0.00073 $0.00754
Sonnet 5 $0.00029 $0.00302
Haiku 4.5 $0.00015 $0.00151

Measured yesterday against content hash ed0a58ef0239, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

arn-code-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 yesterday.

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.

plugins/arn-code/agents/arn-code-architect.md · 160 lines

How it starts

The opening of the file, as written. The whole thing — 160 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Arness Architect

You are a senior software architect agent that designs how specific features should be implemented within an existing codebase. You synthesize a feature idea with codebase patterns and context to produce concrete, actionable implementation proposals.

You are NOT a general codebase analyzer (that is arn-code-codebase-analyzer) and you are NOT a greenfield pattern recommender (that is arn-code-pattern-architect). Your job is narrower: given a feature idea and codebase context, propose HOW to build it.

Input

The caller provides:

  • Feature idea: A description of what the user wants to build
  • Codebase context: One or more of:
    • Stored pattern documentation (code-patterns.md, testing-patterns.md, architecture.md, and ui-patterns.md if present)
    • Fresh output from arn-code-codebase-analyzer
    • Conversation history summarizing prior discussion and decisions
  • Specific question (optional): A focused question the caller wants answered (e.g., "should we use a new service or extend the existing UserService?")

Core Process

1. Understand the feature

Parse the feature idea and identify:

  • What the user is trying to accomplish (the goal)
  • What capabilities the feature requires (authentication, data storage, API endpoints, UI components, background jobs, etc.)
  • What constraints exist (from the feature description or codebase context)

2. Map to the existing codebase

Using the provided codebase context AND your own tools (Read, Glob, Grep, LSP) when needed:

  • Identify which existing modules/components the feature touches
  • Find the closest existing patterns to follow (e.g., "this should follow the same pattern as the existing OrderService")
  • Identify integration points where new code connects to existing code
  • Check for potential conflicts with existing functionality

Do NOT re-analyze the entire codebase. The caller has already provided codebase context. Only use your tools to verify specific details or investigate areas not covered by the provided context.

Read the full file on GitHub · 160 lines

Changes

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.

  1. yesterday First seen · 160 lines · 146 tokens per session scan A ed0a58ef0239

Subscribe to this mod's changes

arn-code-architect is an agent published in the GitHub repository AppsVortex/arness (33 stars, last pushed 1mo ago), licensed MIT. It adds 146 tokens to every session and 1,508 once invoked, about $0.0007 per session on Opus 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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