A technical-design workflow that turns approved requirements into a `design.md` specification. It explains how the feature will be built, including architecture, components, data, APIs, flows, edge cases, decisions, risks, and implementation questions.

Use it to define the technical approach for a feature in `.ai/sdd/specs/NNN-feature-name/`. It is for deciding how approved requirements should work in code and systems.

It gives implementers enough technical detail to proceed without guessing while keeping the requirements separate from implementation choices. It also checks that the requirements have been approved before design starts.

sdd-spec — Skill for Claude Code and Codex by felipefontoura

Install

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.

Any agent

npx skills add felipefontoura/pi-sdd-kit --skill sdd-spec

Clone the repo

git clone --depth 1 https://github.com/felipefontoura/pi-sdd-kit

Made for: Claude Code, Codex.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/felipefontoura/pi-sdd-kit/sdd-spec/github.svg)](https://agentmods.dev/skills/felipefontoura/pi-sdd-kit/sdd-spec)

Your own site

<a href="https://agentmods.dev/skills/felipefontoura/pi-sdd-kit/sdd-spec"><img src="https://agentmods.dev/badge/skills/felipefontoura/pi-sdd-kit/sdd-spec/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/felipefontoura/pi-sdd-kit/sdd-spec"><img src="https://agentmods.dev/badge/skills/felipefontoura/pi-sdd-kit/sdd-spec.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 70 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,075 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00070	$0.01075
Opus 5	$0.00035	$0.00537
Sonnet 5	$0.00014	$0.00215
Haiku 4.5	$0.00007	$0.00108

Measured 9d ago against content hash 8f237c1283f4, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

sdd-spec 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 9d 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.

skills/sdd-spec/SKILL.md · 88 lines

How it starts

The opening of the file, as written. The whole thing — 88 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SDD Spec / Design

Translate approved requirements into a practical technical design.

Purpose

Design defines how the approved requirements will be implemented. It should be detailed enough for an implementer to work without guessing, but lightweight enough for small and medium projects.

Workflow

Load the SDD reference.
- Read ../_shared/references/sdd-practical.md.
- Apply the Language Policy: respond and write artifacts in the user's initial chat language while keeping skill instructions and templates in EN-US.
- Read ../_shared/references/templates.md when drafting the artifact.
- Use package-level templates/design.md as the user-facing template when available.
- Load relevant .ai/steering/*.md files when present, especially product.md, tech-stack.md, conventions.md, and principles.md.
Locate the feature and validate the gate.
- Use .ai/sdd/specs/NNN-feature-name/.
- Read .status.
- Validate .status against the official status values from sdd-practical.md.
- If .status is missing or invalid, stop and ask the user to repair it; do not infer approval from requirements.md existing.
- Block if status is not requirements:approved, unless the user explicitly asks for a non-binding draft spike.
- If blocked, report the current status and recommend /skill:sdd-prd approval as the next safe action.
- Read requirements.md completely.
Explore project context.
- Inspect existing code, conventions, routing, components, services, tests, and build tooling relevant to the feature.
- Prefer existing patterns over new abstractions.
- Identify likely files and integration points, but do not generate tasks yet.
Clarify technical choices.
- Ask one question at a time when decisions require user input.
- Present 2-3 approaches for meaningful trade-offs.
- Cover component/module boundaries, state/data ownership, API/integration boundaries, testing approach, and operational risks where relevant.

Read the full file on GitHub · 88 lines

Changes

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.

9d ago First seen · 88 lines · 70 tokens per session scan A 8f237c1283f4

Subscribe to this mod's changes

sdd-spec is a skill published in the GitHub repository felipefontoura/pi-sdd-kit (22 stars, last pushed 2mo ago), licensed MIT. It adds 70 tokens to every session and 1,075 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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