Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/ValorVie/custom-skillsnpx agentmods add skills/valorvie/custom-skills/forward-derivationWrote 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/valorvie/custom-skills/forward-derivation)<a href="https://agentmods.dev/skills/valorvie/custom-skills/forward-derivation"><img src="https://agentmods.dev/badge/skills/valorvie/custom-skills/forward-derivation/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/valorvie/custom-skills/forward-derivation"><img src="https://agentmods.dev/badge/skills/valorvie/custom-skills/forward-derivation.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00091 | $0.03595 |
| Opus 5 | $0.00046 | $0.01798 |
| Sonnet 5 | $0.00018 | $0.00719 |
| Haiku 4.5 | $0.00009 | $0.00360 |
Grade A, and why
forward-derivation 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 6d 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 — 472 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Forward Derivation Guide
Language: English | 繁體中文
Version: 2.0.0 Last Updated: 2026-01-25 Applicability: Claude Code Skills
Core Standard: This skill implements Forward Derivation Standards. For comprehensive methodology documentation accessible by any AI tool, refer to the core standard.
Purpose
This skill guides you through deriving BDD scenarios and TDD test skeletons from approved SDD specifications, with strict adherence to Anti-Hallucination standards.
Note: ATDD test tables are optional and available via
/derive-atdd. BDD scenarios already serve as executable acceptance tests, making ATDD tables redundant for most use cases.
Forward Derivation is the symmetrical counterpart to Reverse Engineering:
- Reverse Engineering: Code → Specification
- Forward Derivation: Specification → Tests
Quick Reference
Forward Derivation Workflow
┌─────────────────────────────────────────────────────────────────┐
│ Forward Derivation Workflow │
├─────────────────────────────────────────────────────────────────┤
│ │
│ 1️⃣ SPEC Parsing (AI Automated) │
│ ├─ Read approved specification │
│ ├─ Extract Acceptance Criteria (GWT or bullet) │
│ └─ Validate SPEC structure and completeness │
│ │
│ 2️⃣ Derivation (AI Automated) │
│ ├─ AC → BDD Gherkin scenarios │
│ ├─ AC → TDD test skeletons with TODOs │
│ └─ (Optional) AC → ATDD acceptance test tables │
│ │
│ 3️⃣ Human Review (Required) │
│ ├─ Verify generated scenarios match AC intent │
│ ├─ Fill in [TODO] sections │
│ └─ Refine step definitions if needed │
│ │
└─────────────────────────────────────────────────────────────────┘
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.
- 6d ago First seen · 472 lines · 91 tokens per session scan A 7b64853a9af8
forward-derivation is a skill published in the GitHub repository ValorVie/custom-skills (5 stars, last pushed 2d ago), licensed MIT. It adds 91 tokens to every session and 3,595 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 2026-09-03.
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