refactor-safely

A method for reorganizing code without intentionally changing what it does. A refactor changes structure, such as moving or renaming code, while preserving behavior.

In plain words
What is it for?
Use it when extracting functions, renaming symbols, splitting modules, or replacing an implementation while keeping the same behavior.
Why use it?
It reduces the chance that cleanup work introduces bugs by requiring tests, small changes, and verification after each step.

Skill for Claude CodeCodex

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 skills/buildmoonshot/skillpacks/refactor-safely
Any agent
npx skills add buildmoonshot/skillpacks --skill refactor-safely
Clone the repo
git clone --depth 1 https://github.com/buildmoonshot/skillpacks

Made for: Claude Code, Codex.

Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 443 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 $0.00066 $0.00443
Opus 5 $0.00033 $0.00221
Sonnet 5 $0.00013 $0.00089
Haiku 4.5 $0.00007 $0.00044

Measured 2d ago against content hash 91c9d8910102, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

refactor-safely 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 2d 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.

skills/engineering/expert/refactor-safely/SKILL.md · 28 lines

What it actually says

Refactor Safely

A refactor changes structure, not behavior. The whole risk is changing behavior by accident. Defend against it.

The procedure

  1. Pin the behavior first. Before touching anything, make sure the code you're about to move is covered by tests. If it isn't, write characterization tests that capture what it currently does (even quirks) and get them green. You cannot refactor safely what you cannot observe.

  2. Refactor in small steps. Make one structural change at a time — extract a function, rename a symbol, move a file. Keep each step mechanical and reversible.

  3. Run the tests after every step. Green after each step means the behavior held. If a step goes red, you know exactly which change broke it — revert just that step.

  4. Keep refactor commits separate from behavior changes. Never mix "I reorganized this" with "I also fixed a bug / changed logic" in the same diff. A reviewer should be able to trust a refactor diff changes nothing functional. If you spot a real bug mid-refactor, note it and handle it in its own change.

Signs you've left "refactor" and entered "rewrite"

  • The tests need to change to keep passing → you're altering behavior, not refactoring. Stop and make that an explicit, separate decision.
  • The diff is large and you can't point to the equivalent old code for each new line → break it into smaller steps.

Why this matters

"Just cleaning this up" is one of the most common ways working software breaks, because the change feels safe and goes unreviewed. Characterization tests plus small, individually-verified steps turn a risky sweep into a sequence of provably-behavior-preserving moves.

Files

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.

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. 2d ago First seen · 28 lines · 66 tokens per session scan A 91c9d8910102

Subscribe to this mod's changes

refactor-safely is a skill published in the GitHub repository buildmoonshot/skillpacks (2 stars, last pushed 2mo ago), licensed MIT. It adds 66 tokens to every session and 443 once invoked, about $0.0003 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 2026-08-31.

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