spec-driven-development

spec-driven-development is a skill for Claude Code, Codex from Threat-Vector-Security/guardian-agent. It costs 43 tokens per session (1,675 once invoked), scanned A, a copy of as-spec-driven-development, Apache-2.0.

A development workflow that writes and reviews a specification before planning tasks and coding. The specification records what is being built, why, and how completion will be judged.

In plain words
What is it for?
Starting projects or significant features, clarifying ambiguous requirements, planning changes across multiple files, and making architectural decisions.
Why use it?
It turns vague or incomplete requirements into an agreed description before implementation begins. This reduces guesswork and exposes assumptions early.

Skill for Claude CodeCodex

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/threat-vector-security/guardian-agent/spec-driven-development
Any agent
npx skills add Threat-Vector-Security/guardian-agent --skill spec-driven-development
Clone the repo
git clone --depth 1 https://github.com/Threat-Vector-Security/guardian-agent

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.

agentmods badge for spec-driven-development

README.md
[![agentmods](https://agentmods.dev/badge/skills/threat-vector-security/guardian-agent/spec-driven-development.svg)](https://agentmods.dev/skills/threat-vector-security/guardian-agent/spec-driven-development)
Your own site
<a href="https://agentmods.dev/skills/threat-vector-security/guardian-agent/spec-driven-development"><img src="https://agentmods.dev/badge/skills/threat-vector-security/guardian-agent/spec-driven-development.svg" alt="Measured on agentmods" height="20"></a>
Per session 43 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,675 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 80% copy Near-identical to another mod 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 $0.00043 $0.01675
Opus 5 $0.00022 $0.00838
Sonnet 5 $0.00009 $0.00335
Haiku 4.5 $0.00004 $0.00168

Measured 3d ago against content hash 6d098845420d, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

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 3d 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.

Origin

This is a copy

80% identical to as-spec-driven-development — 18 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/spec-driven-development/SKILL.md · 201 lines

How it starts

The opening of the file, as written. The whole thing — 201 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Spec-Driven Development

Overview

Write a structured specification before writing any code. The spec is the shared source of truth between you and the human engineer — it defines what we're building, why, and how we'll know it's done. Code without a spec is guessing.

When to Use

  • Starting a new project or feature
  • Requirements are ambiguous or incomplete
  • The change touches multiple files or modules
  • You're about to make an architectural decision
  • The task would take more than 30 minutes to implement

When NOT to use: Single-line fixes, typo corrections, or changes where requirements are unambiguous and self-contained.

The Gated Workflow

Spec-driven development has four phases. Do not advance to the next phase until the current one is validated.

SPECIFY ──→ PLAN ──→ TASKS ──→ IMPLEMENT
   │          │        │          │
   ▼          ▼        ▼          ▼
 Human      Human    Human      Human
 reviews    reviews  reviews    reviews

Phase 1: Specify

Start with a high-level vision. Ask the human clarifying questions until requirements are concrete.

Surface assumptions immediately. Before writing any spec content, list what you're assuming:

ASSUMPTIONS I'M MAKING:
1. This is a web application (not native mobile)
2. Authentication uses session-based cookies (not JWT)
3. The database is PostgreSQL (based on existing Prisma schema)
4. We're targeting modern browsers only (no IE11)
→ Correct me now or I'll proceed with these.

Don't silently fill in ambiguous requirements. The spec's entire purpose is to surface misunderstandings before code gets written — assumptions are the most dangerous form of misunderstanding.

Write a spec document covering these six core areas:

  1. Objective — What are we building and why? Who is the user? What does success look like?

  2. Commands — Full executable commands with flags, not just tool names.

    Build: npm run build
    Test: npm test -- --coverage
    Lint: npm run lint --fix
    Dev: npm run dev
    

Read the full file on GitHub · 201 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. 3d ago First seen · 201 lines · 43 tokens per session scan A 6d098845420d

Subscribe to this mod's changes

spec-driven-development is a skill published in the GitHub repository Threat-Vector-Security/guardian-agent (11 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 43 tokens to every session and 1,675 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. It is 80% identical to as-spec-driven-development, differing in 18 lines, and is treated as a copy.

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