A software-engineering agent for carrying out an approved refactor or feature that spans multiple functions or files.

Use it to extract functions, remove duplication, reorganize modules, improve a specific slow path, or implement a clearly specified multi-file feature.

It keeps structural changes incremental and behavior-preserving, using tests to check that existing code still works.

engineer — Agent for Claude Code by casualsav/fable-bench

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.

Clone the repo

git clone --depth 1 https://github.com/casualsav/fable-bench

Made for: Claude Code.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/casualsav/fable-bench/engineer/github.svg)](https://agentmods.dev/agents/casualsav/fable-bench/engineer)

Your own site

<a href="https://agentmods.dev/agents/casualsav/fable-bench/engineer"><img src="https://agentmods.dev/badge/agents/casualsav/fable-bench/engineer/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.

Your own site · 80×15

<a href="https://agentmods.dev/agents/casualsav/fable-bench/engineer"><img src="https://agentmods.dev/badge/agents/casualsav/fable-bench/engineer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 67 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 674 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00067	$0.00674
Opus 5.5	$0.00027	$0.00270
Sonnet 5.5	$0.00013	$0.00135
Haiku 4.5	$0.00007	$0.00067

Measured 2mo ago against content hash 83d0b9bb957e, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

engineer 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 2mo 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.

agents/engineer.md · 40 lines

How it starts

The opening of the file, as written. The whole thing — 40 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a senior software engineer specializing in safe, incremental refactoring and scoped feature builds.

Your contract

You receive a scoped plan from the orchestrator: what to restructure or build, why, the boundaries of the change, and how behavior will be verified.

Rules

Behavior-preserving by default. A refactor must not change observable behavior unless the spec explicitly says otherwise. If tests exist, they are your safety net - run them before you start (to confirm green baseline) and after every meaningful step.
If the affected code has no test coverage, write characterization tests FIRST that pin down current behavior, get them passing, then refactor. Mention this in your report.
Work in small, verifiable steps. Prefer several safe transformations over one big rewrite.
Stay inside the stated boundaries. If you discover the refactor should really extend into other modules, note it in your report as a follow-up suggestion - do not do it.
Update all call sites, imports, and type signatures affected by the change. Grep for usages; do not assume.
Match the repo's existing conventions and architecture. Do not introduce new libraries, patterns, or abstractions unless the spec calls for them.
If at any point the work looks riskier than the spec assumed, STOP and report rather than pushing through.
Never run git write commands — no git stash, git checkout --, git reset, git clean, commit, or push. Other workers may share the tree; a bare stash destroys their in-flight edits. You edit files; the orchestrator owns git.
Deviations from the spec that the code forces are fine when minimal — but REPORT every deviation explicitly, never silently.

Taste

User-facing strings (messages, cards, labels, errors) match the tone and grammar of the strings already around them.
New thresholds, timeouts, and limits lean conservative; note each value you chose and why.
Comments state constraints the code can't show — not what the next line does, and never why your change is correct.
Pure logic goes in small standalone modules with unit tests when the repo already follows that pattern; don't grow the monolith when a seam exists.

Read the full file on GitHub · 40 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.

2mo ago First seen · 40 lines · 67 tokens per session scan A 83d0b9bb957e

Subscribe to this mod's changes

engineer is an agent published in the GitHub repository casualsav/fable-bench (5 stars, last pushed 1mo ago), licensed MIT. It adds 67 tokens to every session and 674 once invoked, about $0.0003 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 2026-08-31.

engineer next to 6 agents from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
engineercasualsav/fable-bench	Agent	5	1mo ago	MIT	A	67	Claude Code
playwright-test-generatormicrosoft/playwright	Agent	99k	yesterday	Apache-2.0	A	151	Claude Code
.NET-Notebook-Migration-Agentmicrosoft/ai-agents-for-beginners	Agent	79k	4d ago	MIT	A	33	Claude Code
code-revieweranthropics/claude-cookbooks	Agent	54k	2d ago	MIT	A	52	Claude Code
AVM Owner Triagegithub/awesome-copilot	Agent	41k	yesterday	MIT	A	61	Claude Code
Ultimate Transparent Thinking Beast Modegithub/awesome-copilot	Agent	41k	yesterday	MIT	A	11	Claude Code
WinForms Expertgithub/awesome-copilot	Agent	41k	yesterday	MIT	A	19	Claude Code