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/juanmhidalgo/claude-plugins/spec-driven-developmentnpx skills add juanmhidalgo/claude-plugins --skill spec-driven-developmentgit clone --depth 1 https://github.com/juanmhidalgo/claude-pluginsWrote 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/juanmhidalgo/claude-plugins/spec-driven-development)<a href="https://agentmods.dev/skills/juanmhidalgo/claude-plugins/spec-driven-development"><img src="https://agentmods.dev/badge/skills/juanmhidalgo/claude-plugins/spec-driven-development.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 | $0.00048 | $0.02516 |
| Opus 5 | $0.00024 | $0.01258 |
| Sonnet 5 | $0.00010 | $0.00503 |
| Haiku 4.5 | $0.00005 | $0.00252 |
Grade A, and why
spec-driven-development 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 today.
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 — 208 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Spec-Driven Development
When to Use
- Starting a new feature or project
- Requirements are ambiguous or incomplete
- Change touches multiple files or modules
- Task would take more than 30 minutes to implement
- About to make an architectural decision
The Gated Workflow
Four phases. Do not advance until the current phase is validated by the user.
SPECIFY ──→ PLAN ──→ TASKS ──→ IMPLEMENT
│ │ │ │
▼ ▼ ▼ ▼
Review Review Review Review
Phase 1: Specify
Surface assumptions immediately before writing anything:
ASSUMPTIONS I'M MAKING:
1. This is a web application (not native mobile)
2. Authentication uses session-based cookies
3. The database is PostgreSQL
→ Correct me now or I'll proceed with these.
Write a spec covering eight areas:
- Objective — What, why, who
- Acceptance Criteria — A dedicated, scannable section of observable, user-facing criteria (do not bury them in Objective). Include at least one failure/error-state criterion, not only happy-path outcomes. This is what downstream review, planning, and QA anchor to.
- Commands — Full executable commands (build, test, lint, dev)
- Project Structure — Where source, tests, and docs live
- Code Style — One real snippet showing conventions
- Testing Strategy — Framework, location, coverage, test levels (the engineering view)
- QA Checklist — A separate, QA-facing list grouped as happy path / edge cases / error states; distinct from the engineering-oriented Testing Strategy. Every error-state acceptance criterion gets a matching check.
- Boundaries — Always do / Ask first / Never do
Reframe vague requirements as testable success criteria. Ban these words from acceptance criteria unless you immediately define them concretely: fast, slow, easy, simple, user-friendly, intuitive, seamless, better, improved.
"Make the dashboard faster"
→ LCP < 2.5s on 4G, initial data load < 500ms, CLS < 0.1
→ Are these the right targets?
"Make onboarding intuitive"
→ ≥80% of new users complete the first three steps without help-text dwell > 3s
→ Or: define what "intuitive" means here in plain language.
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.
- today First seen · 208 lines · 48 tokens per session scan A 4a7b5a24ec70
spec-driven-development is a skill published in the GitHub repository juanmhidalgo/claude-plugins (8 stars, last pushed 9d ago), licensed MIT. It adds 48 tokens to every session and 2,516 once invoked, about $0.0002 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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