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.
npx agentmods add skills/caiaffa/claude-code-ultimate-engineering-system/safe-refactoringnpx skills add caiaffa/claude-code-ultimate-engineering-system --skill safe-refactoringgit clone --depth 1 https://github.com/caiaffa/claude-code-ultimate-engineering-systemWrote 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/caiaffa/claude-code-ultimate-engineering-system/safe-refactoring)<a href="https://agentmods.dev/skills/caiaffa/claude-code-ultimate-engineering-system/safe-refactoring"><img src="https://agentmods.dev/badge/skills/caiaffa/claude-code-ultimate-engineering-system/safe-refactoring.svg" alt="Measured on agentmods" height="20"></a>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 | $0.00025 | $0.00590 |
| Opus 5 | $0.00013 | $0.00295 |
| Sonnet 5 | $0.00005 | $0.00118 |
| Haiku 4.5 | $0.00003 | $0.00059 |
Grade A, and why
safe-refactoring 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 3d 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 — 61 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Mission
Improve code structure without silently changing system behavior or increasing delivery risk.
When to use
- Cleaning up legacy code.
- Extracting modules or services.
- Reducing coupling.
- Introducing clearer abstractions.
- Reorganizing domain boundaries.
Handoff
- Receives from: code-reviewer (identified tech debt) or backend-platform-engineer (planned improvement).
- Hands off to: test-strategy (protective tests), code-reviewer (review the refactor), release-commander (if affects production behavior).
The safe refactoring method
1. CHARACTERIZE → Write tests that capture current behavior (before changing anything)
2. IDENTIFY → What exactly needs to change? What must stay the same?
3. PLAN → Break the refactor into small, independently-mergeable steps
4. EXECUTE → One step at a time. Each step: green tests → change → green tests
5. VALIDATE → Run full test suite. Check no behavioral regression.
6. DEPLOY → Ship incrementally. Monitor for unexpected changes.
Refactor vs rewrite decision
| Choose refactor when | Choose rewrite when |
|---|---|
| Core behavior is correct, structure is bad | Core behavior is wrong |
| Tests exist or can be written | System is so tangled tests can't be written |
| Team needs to maintain it during refactor | Clean break is possible (new service, new module) |
| Incremental delivery is possible | All-or-nothing is the only realistic path |
Default to refactor. Rewrites are almost always more expensive than estimated.
Common refactoring pitfalls
- Changing behavior accidentally while restructuring.
- Removing "unused" code that's actually called via reflection or config.
- Breaking error semantics (different exception types, different HTTP codes).
- Changing timing that affects distributed flows.
- Losing observability (spans, metrics, log lines removed).
Red flags — stop and reassess if
- You can't write a characterization test for the current behavior.
- The refactor touches more than 3 modules simultaneously.
- The refactor requires coordinated changes across services.
- There's no way to deploy the refactor incrementally.
- You find yourself saying "while we're at it, let's also..."
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.
- 3d ago First seen · 61 lines · 25 tokens per session scan A eb4592945b2d
safe-refactoring is a skill published in the GitHub repository caiaffa/claude-code-ultimate-engineering-system (17 stars, last pushed 2mo ago), licensed MIT. It adds 25 tokens to every session and 590 once invoked, about $0.0001 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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