Borrowing it
Nothing to install: this file belongs to timothywarner/copilot-dev. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/timothywarner/copilot-dev/main/.github/skills/legacy-code-refactor/SKILL.mdgit clone --depth 1 https://github.com/timothywarner/copilot-devWrote 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/skills/timothywarner/copilot-dev/legacy-code-refactor)<a href="https://agentmods.dev/skills/timothywarner/copilot-dev/legacy-code-refactor"><img src="https://agentmods.dev/badge/skills/timothywarner/copilot-dev/legacy-code-refactor/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/skills/timothywarner/copilot-dev/legacy-code-refactor"><img src="https://agentmods.dev/badge/skills/timothywarner/copilot-dev/legacy-code-refactor.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00085 | $0.02387 |
| Opus 5.5 | $0.00034 | $0.00955 |
| Sonnet 5.5 | $0.00017 | $0.00477 |
| Haiku 4.5 | $0.00009 | $0.00239 |
Grade A, and why
legacy-code-refactor 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.
How it starts
The opening of the file, as written. The whole thing — 275 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Legacy Code Refactor Skill
You are an expert in safely modernizing legacy JavaScript/TypeScript codebases. When this skill activates, follow the five-step methodology below precisely. Never change observable behavior — only improve the structure, readability, and maintainability.
The Core Principle
"Refactoring is changing the internal structure of software without changing its observable behavior." — Martin Fowler
Every transformation must be provably safe: the code must do the same thing before and after.
Step 1: Audit — Identify All Anti-Patterns
Read the target file completely, then produce an audit table listing every issue found:
| # | Line | Anti-Pattern | Why It's a Problem | Safe Fix |
|---|---|---|---|---|
| 1 | 3 | var in function scope |
var is function-scoped and hoisted; causes subtle bugs |
Replace with const or let |
| 2 | 12 | Nested callback (callback hell) | Impossible to reason about error flow; unreadable | Rewrite with async/await |
| 3 | 25 | prototype method |
No encapsulation; harder to subclass; verbose | Convert to class with methods |
| 4 | 31 | Magic number 86400000 |
Intent is invisible; breaking change if the value changes | Extract to named constant MS_PER_DAY |
| 5 | 44 | No error handling | Unhandled rejections crash Node.js silently | Wrap in try/catch |
| 6 | 55 | Mixed concerns | Validation + persistence + response in one function | Separate into distinct functions |
Present this table to the user before making any changes.
Step 2: Catalog of Anti-Patterns and Safe Fixes
2.1 var → const / let
// BEFORE — var is function-scoped and hoisted; assignment in loops leaks
var maxRetries = 3;
var i;
for (var i = 0; i < maxRetries; i++) { ... }
// AFTER — const for values that don't change, let for loop variables
const MAX_RETRIES = 3;
for (let i = 0; i < MAX_RETRIES; i++) { ... }
Safe when: The variable is not re-declared in the same scope (var allows re-declaration; let/const do not).
What ships with it
2 files 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.
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 · 275 lines · 85 tokens per session scan A 55fc9357475d
legacy-code-refactor is a skill published in the GitHub repository timothywarner/copilot-dev (46 stars, last pushed 1mo ago), licensed MIT. It adds 85 tokens to every session and 2,387 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 2026-08-30.
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