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/leejuoh/claude-code-zero/duck-reviewnpx skills add LeeJuOh/claude-code-zero --skill duck-reviewgit clone --depth 1 https://github.com/LeeJuOh/claude-code-zeroWrote 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/leejuoh/claude-code-zero/duck-review)<a href="https://agentmods.dev/skills/leejuoh/claude-code-zero/duck-review"><img src="https://agentmods.dev/badge/skills/leejuoh/claude-code-zero/duck-review.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 5.1 | $0.00060 | $0.00713 |
| Opus 5 | $0.00030 | $0.00357 |
| Sonnet 5 | $0.00012 | $0.00143 |
| Haiku 4.5 | $0.00006 | $0.00071 |
Grade A, and why
duck-review 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 5d 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 — 62 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Duck — PR / Change Review Mode
Read first: ../ducking/engine.md — persona, "Wait for their answer", Confidence Check (PR/Change Review row), Branch-first workflow, Intensity Scaling, Uncertainty Check, Session Wrap-up + gap persistence, Facilitation, Gotchas. They apply here.
Input: Run git diff (or git diff --staged, or PR diff).
Flow
- One-sentence summary — always ground the question in the diff's scope:
Your turn: You touched [list the changed files/areas from the diff]. Summarize this entire change in one sentence — what does it do?
- Drill into 2-3 key changes from the diff:
Your turn: In [file:line_range], you changed [specific thing]. Why?
- Impact assessment:
Your turn: What existing behavior could this change break? Where should we look?
→ Then run the Temporal cost simulation subsection below before moving on.
- Generation vs comparison (when appropriate):
Your turn: For [the problem this code solves] — how would you have approached it?
After their answer, compare with the actual implementation. Discuss trade-offs.
- Confidence check — run the PR/Change Review row from the Confidence Check (shared) table.
Temporal cost simulation
Frame the change on a 6-month horizon, not just "does it work now":
Your turn: Six months from now, someone — maybe future you — has to modify this code. Where's it going to hurt first? Why?
Follow-ups depending on their answer:
- Names a specific file/function → "Why is that spot fragile? What assumption in the current structure breaks first?"
- "Nothing feels fragile" → "What's that confidence based on? What abstraction in this diff guarantees that?"
- Vague ("kind of everywhere") → "Just one spot. If you commit this now, what's the first thing you'll regret?"
Question Frameworks
Assumptions — "What has to be true for this change to hold up?" Surface dependencies on other code, data formats, or system state.
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.
- 5d ago First seen · 62 lines · 60 tokens per session scan A 35f2f0b5a5de
duck-review is a skill published in the GitHub repository LeeJuOh/claude-code-zero (51 stars, last pushed 6d ago), licensed MIT. It adds 60 tokens to every session and 713 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 2026-08-30.
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