spec-design

spec-design is a skill for Claude Code, Codex from alanvaa06/forge-master. It costs 109 tokens per session (1,311 once invoked), scanned A, original, MIT.

A guide that turns an approved product requirements document into a technical design specification. It defines the architecture, components, interfaces, file layout, decisions, and risks before detailed implementation planning.

In plain words
What is it for?
Use it for projects with multiple components, new or changed data models or APIs, architectural trade-offs, or a history of design inconsistencies; small, obvious tasks may skip it.
Why use it?
It prevents separate implementation phases from making conflicting design decisions. It also creates a human review point for larger changes before work is broken into tasks.

Skill for Claude CodeCodex

Part of the forge-master plugin — 7 skills shipped together

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.

agentmods
npx agentmods add skills/alanvaa06/forge-master/spec-design
Any agent
npx skills add alanvaa06/forge-master --skill spec-design
Clone the repo
git clone --depth 1 https://github.com/alanvaa06/forge-master

Made for: Claude Code, Codex.

Or install forge-master, the plugin that ships this one along with the rest of its 7 skills.

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.

agentmods badge for spec-design

README.md
[![agentmods](https://agentmods.dev/badge/skills/alanvaa06/forge-master/spec-design.svg)](https://agentmods.dev/skills/alanvaa06/forge-master/spec-design)
Your own site
<a href="https://agentmods.dev/skills/alanvaa06/forge-master/spec-design"><img src="https://agentmods.dev/badge/skills/alanvaa06/forge-master/spec-design.svg" alt="Measured on agentmods" height="20"></a>
Per session 109 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,311 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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.

ModelPer sessionOnce invoked
Fable 5 $0.00109 $0.01311
Opus 5 $0.00055 $0.00656
Sonnet 5 $0.00022 $0.00262
Haiku 4.5 $0.00011 $0.00131

Measured 4d ago against content hash 3e0c0565af7a, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

spec-design 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.

skills/spec-design/SKILL.md · 55 lines

How it starts

The opening of the file, as written. The whole thing — 55 lines — stays where its author put it; the contents beside it link to each section on GitHub.

spec-design — PRD to Technical Design (Human Gate 1.5)

Produce docs/forge/specs/spec-NNN.md from an approved docs/forge/prd/NNN-name.md: the HOW that sits between the PRD's WHAT and the plan's WHEN. Decisions get made once here, so phase subagents never re-derive architecture inconsistently.

This step is OPTIONAL by design. The loop's philosophy is optimistic defaults — if the task looks small (few phases, obvious structure, no new interfaces), say so and ASK the user as a lettered list (mark one Recommended with a concrete why), never decide yourself:

This task looks small. Proceed with the spec? a) Skip the spec, go straight to /forge-master:plan-designRecommended, small task with obvious structure b) Write the spec anyway — you want the design locked before planning

A spec is warranted when any of: multiple components must agree on interfaces, a data model or API contract is being introduced/changed, the PRD's Constraints imply architectural tradeoffs, or lessons.md shows past runs failing on design drift — when these hold, recommend (b) instead. The user picks by replying with a letter.

Subordination rule: the plan (plan-NNN.md) is the ONLY execution contract. The spec is a design reference the plan cites — if they ever conflict, the plan wins and the spec gets corrected.

Step 1 — Load inputs

  • Read the approved PRD docs/forge/prd/NNN-name.md (ask which N if ambiguous). Do not start without an approved PRD — ACs drive the design.
  • Read docs/context/memory.md (existing architecture decisions bind you) and docs/context/lessons.md (past design-related friction).
  • For an existing codebase: scan the repo structure and conventions — the spec extends what exists, it does not invent a parallel architecture.
  • Read templates/spec-template.md (from this plugin) as the output skeleton.

Step 2 — Design

Fill the template's sections, anchored to PRD IDs throughout:

Read the full file on GitHub · 55 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.

  1. 4d ago First seen · 55 lines · 109 tokens per session scan A 3e0c0565af7a

Subscribe to this mod's changes

spec-design is a skill published in the GitHub repository alanvaa06/forge-master (1 stars, last pushed 1mo ago), licensed MIT. It adds 109 tokens to every session and 1,311 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 2026-08-31.