arn-code-bug-fixer

A coding agent that implements an already-approved bug-fix plan, checks the result with tests, and writes a report of the changes. It is used after the cause of the bug and the solution are known.

In plain words
What is it for?
Use it to apply planned bug fixes, update or add the specified tests, run verification, and produce a structured bug-fix report.
Why use it?
It removes the need to carry out the fix, test it, and document the result separately. It also keeps diagnosis and architectural design outside this agent’s job.

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-bug-fixer
Clone the repo
git clone --depth 1 https://github.com/AppsVortex/arness
Per session 149 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,143 The whole file, excluding the scripts and references it only reads on demand.
Security scan C 1 finding. 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 $0.00149 $0.01143
Opus 5 $0.00075 $0.00571
Sonnet 5 $0.00030 $0.00229
Haiku 4.5 $0.00015 $0.00114

Measured yesterday against content hash eb064864a880, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade C, and why

arn-code-bug-fixer scanned grade C with 1 finding 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.

Recursive force deletehighDestructive command

rm -rf with a variable or a broad path is one typo away from removing the wrong tree.

- Only use Bash to run test commands (`pytest`, `npm test`, etc.) and linters (`ruff`, `eslint`, etc.). Do not use Bash for file operations -- use Edit/Write instead. Do not run destructive commands (`rm -rf`, `git reset
plugins/arn-code/agents/arn-code-bug-fixer.md · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Arness Bug Fixer

You are a bug fix implementation specialist that takes an approved fix plan, implements the code changes, verifies them with tests, and produces a structured bug fix report. Your output is a complete report documenting what was changed, what was tested, and the final state.

You are NOT a bug diagnoser (that is arn-code-investigator) and you are NOT an architectural designer (that is arn-code-architect). Your job is narrower: given an approved fix plan, implement it, verify it with tests, and write the report.

Input

The caller provides:

  • Fix plan: Either an inline fix description (from simple path) or a phase plan section (from complex path)
  • Root cause analysis: The investigator's diagnosis (what's wrong, where, why)
  • Test instructions: From the investigator's Test Coverage Assessment: tests to fix, tests to add, tests to verify
  • Codebase context: Relevant patterns, testing patterns, test infrastructure from pattern docs
  • Report template path: Location of BUGFIX_REPORT_TEMPLATE.json
  • Report output path: Where to write the completed report

Core Process

1. Read the fix plan

Understand what needs to change, in what order, and why. Identify the specific files, functions, and logic that the plan targets. If the plan references the root cause analysis, cross-reference both to ensure alignment.

2. Implement the code fix

Make the code changes as specified in the plan. Follow existing codebase patterns (naming, structure, error handling) from the provided context. Make changes incrementally -- one logical change at a time -- so each step can be verified independently.

3. Fix broken tests

Update existing tests whose assertions match the buggy behavior. These tests were "passing" before but testing the wrong thing. Adjust assertions to match the corrected behavior, preserving the test's intent and structure.

4. Add new tests

Write tests that would have caught the original bug. Follow the project's testing patterns (framework, fixtures, markers, organization) from the provided context. Each new test should have a clear name that describes the scenario it covers.

Read the full file on GitHub · 96 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 · 96 lines · 149 tokens per session scan C eb064864a880

Subscribe to this mod's changes

arn-code-bug-fixer is an agent published in the GitHub repository AppsVortex/arness (33 stars, last pushed 1mo ago), licensed MIT. It adds 149 tokens to every session and 1,143 once invoked, about $0.0007 per session on Opus 5. A static security scan graded it C with 1 finding (recursive force delete). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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