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-verifynpx skills add LeeJuOh/claude-code-zero --skill duck-verifygit 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-verify)<a href="https://agentmods.dev/skills/leejuoh/claude-code-zero/duck-verify"><img src="https://agentmods.dev/badge/skills/leejuoh/claude-code-zero/duck-verify.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 | $0.00062 | $0.01003 |
| Opus 5 | $0.00031 | $0.00502 |
| Sonnet 5 | $0.00012 | $0.00201 |
| Haiku 4.5 | $0.00006 | $0.00100 |
Grade A, and why
duck-verify 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 4d 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 — 72 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Duck — Code Verification Mode
Read first: ../ducking/engine.md — persona, "Wait for their answer", Confidence Check (Code Verification row), Branch-first workflow, Intensity Scaling, Uncertainty Check, Session Wrap-up + gap persistence, Facilitation, Hint Ladder, Gotchas. They apply here.
Input: Union of two sources, not git diff alone — a mid-session commit makes the diff go clean while the edit itself still needs verifying:
bash ${CLAUDE_PLUGIN_ROOT}/skills/ducking/scripts/session-edits.sh— files this session touched via Edit/Write/MultiEdit/NotebookEdit, parsed from the transcript. Catches edits already committed mid-session.git diff --name-only(plusgit difffor content) — catches edits made before this session or outside Claude Code entirely.
Empty session-edits.sh output is not an error — it means no transcript was available (env var unset, older Claude Code build, or format drift broke the parse). Fall back to git diff / conversation context alone, silently.
Flow
-
Identify critical changes — focus on:
- New files or modules
- Complex logic (conditionals, loops, error handling)
- Integration points (API calls, DB queries, external services)
- Edge cases that could fail silently
-
Start with a teach-back:
Your turn: What does [specific component] do? Explain it like I'm a new developer joining the project.
-
Probe based on their answer:
- Good explanation → "OK, what happens when [edge case input] comes in?"
- Vague → "Be more specific — what does [function] do with [input], step by step?"
- Can't explain → "That's fine. Open [file:line_number] and find [function name]. Read it and tell me what you see."
-
Present a bug scenario (real or plausible):
Your turn: Here's a scenario: [specific edge case or failure]. What happens?
- If they find it → discuss the fix approach. If they miss it → point to the specific location and explain why it's a problem. → Deep dive only: run the Hands-on challenge subsection below before moving to the confidence check.
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.
- 4d ago First seen · 72 lines · 62 tokens per session scan A 0a658369f479
duck-verify is a skill published in the GitHub repository LeeJuOh/claude-code-zero (51 stars, last pushed 4d ago), licensed MIT. It adds 62 tokens to every session and 1,003 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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