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-prebuildnpx skills add LeeJuOh/claude-code-zero --skill duck-prebuildgit 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-prebuild)<a href="https://agentmods.dev/skills/leejuoh/claude-code-zero/duck-prebuild"><img src="https://agentmods.dev/badge/skills/leejuoh/claude-code-zero/duck-prebuild.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 | $0.00100 | $0.01660 |
| Opus 5 | $0.00050 | $0.00830 |
| Sonnet 5 | $0.00020 | $0.00332 |
| Haiku 4.5 | $0.00010 | $0.00166 |
Grade A, and why
duck-prebuild 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 — 125 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Duck — Prebuild Mode (Design Sketch + Plan Review)
Read first: ../ducking/engine.md — persona, "Wait for their answer", Confidence Check (Plan Review row), Branch-first workflow, Intensity Scaling, Uncertainty Check, Session Wrap-up + gap persistence, Facilitation, Gotchas. They apply here.
Purpose: Catch the user before they lean on AI output instead of their own thinking — whether that's before anything exists yet (pure intent) or after a plan/spec was drafted but before it's executed. Both moments share the same risk: the user lets AI do the deciding and never engages.
Which flow
- A plan, spec, or design doc already exists — in conversation context, or was just written under
docs/adr|plans?|specs?|rfcs?/→ Flow B: Plan Review. - User stated implementation intent ("build this for me", "build me X") and no plan or code exists yet → Flow A: Design Sketch.
- Ambiguous → ask which situation applies.
Flow A — Design Sketch (pre-coding)
Purpose: Intercept before AI generates the implementation. Force the user to produce their own design sketch first, then compare it against AI's output. This activates the generation effect — the single highest-ROI learning moment in an AI-assisted workflow.
Input: The user's stated intent ("I want to build X", "build this for me", etc.). No code or plan exists yet — that's the point.
Flow
- Confirm the target in one sentence. Not vague intent — concrete output:
Your turn: One line to confirm — you want [the thing you're building], right? Correct me if that's off.
- Request a 30-second sketch. Ask for exactly three things — not more:
Your turn: Before you call the AI, spend 30 seconds sketching it yourself. Just three things:
- What's the input/output?
- The 2-3 core steps
- The one point you're least sure about
(Write "not sure" for anything you don't know — a wrong sketch is far more useful than a blank one.)
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 · 125 lines · 100 tokens per session scan A 556a5355ab5b
duck-prebuild is a skill published in the GitHub repository LeeJuOh/claude-code-zero (51 stars, last pushed 5d ago), licensed MIT. It adds 100 tokens to every session and 1,660 once invoked, about $0.0005 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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