spec-driven-dev

A development process that turns a request into a written specification, a technical plan, and a checklist of small tasks. Spec-Driven Development treats the specification as the agreement that the finished code must satisfy.

In plain words
What is it for?
Use it to plan and carry out non-trivial features, major refactors, and structured engineering work with explicit requirements, edge cases, file plans, and verification steps.
Why use it?
It reduces misunderstandings and missed requirements during larger features, refactors, or multi-file changes. It also encourages checking for existing code that can be reused before adding more.

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/amanktyr/tailor/spec-driven-dev
Any agent
npx skills add AmanKtyr/Tailor --skill spec-driven-dev
Clone the repo
git clone --depth 1 https://github.com/AmanKtyr/Tailor

Made for: Claude Code, Codex.

Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,173 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 $0.00035 $0.01173
Opus 5 $0.00017 $0.00587
Sonnet 5 $0.00007 $0.00235
Haiku 4.5 $0.00003 $0.00117

Measured 2d ago against content hash 5f2c87959c60, 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-dev 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 2d 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-driven-dev/SKILL.md · 115 lines

How it starts

The opening of the file, as written. The whole thing — 115 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Spec-Driven Development (SDD) Skill

Activate this skill when creating non-trivial features, refactoring major subsystems, building multi-file modules, or executing structured engineering workflows.

Operational Axiom: The specification is the contract. Reuse is the law. Code is the verifiable artifact.


1. The Spec-Driven Lifecycle

┌────────────────────────────────────────────────────────┐
│ 1. CONSTITUTION: .ai/CONSTITUTION.md                   │
│    Project non-negotiables, intensity, guardrails       │
└───────────────────────────┬────────────────────────────┘
                            │
┌───────────────────────────▼────────────────────────────┐
│ 2. SPECIFICATION: specs/<id>-<name>/spec.md            │
│    User stories, functional requirements, edge cases   │
└───────────────────────────┬────────────────────────────┘
                            │
┌───────────────────────────▼────────────────────────────┐
│ 3. TECHNICAL PLAN: specs/<id>-<name>/plan.md           │
│    AST REUSE AUDIT + file layout + 0-dep verification  │
└───────────────────────────┬────────────────────────────┘
                            │
┌───────────────────────────▼────────────────────────────┐
│ 4. TASK CHECKLIST: specs/<id>-<name>/tasks.md          │
│    Granular task ordering (TRIVIAL -> CRITICAL)        │
└───────────────────────────┬────────────────────────────┘
                            │
┌───────────────────────────▼────────────────────────────┐
│ 5. IMPLEMENTATION & VERIFICATION                       │
│    Atomic changes + unit tests (Exit code: 0)          │
└────────────────────────────────────────────────────────┘

2. Command Reference & Artifact Standards

A. /constitution (.ai/CONSTITUTION.md)

Establishes project-wide architectural principles, intensity mode (lite, balanced, ultra, strict), testing requirements, and forbidden patterns.

B. /spec-new <feature-name> (specs/<id>-<name>/spec.md)

Defines the problem domain and user acceptance criteria:

# Feature: [Feature Name]
**ID:** [001] | **Status:** Draft | Proposed | Approved

## 1. Problem Statement & User Value
Clear explanation of what problem this solves and for whom.

## 2. User Stories & Acceptance Criteria
- As a [role], I want [action] so that [outcome].
  - [ ] Given [precondition], when [action], then [expected result].

## 3. Scope Boundaries
- **In-Scope:** Specific capabilities included in this release.
- **Out-of-Scope:** Explicitly deferred or rejected capabilities.

## 4. Edge Cases & Error Handling
- Network timeouts, missing permissions, invalid payloads, race conditions.

Read the full file on GitHub · 115 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. 2d ago First seen · 115 lines · 35 tokens per session scan A 5f2c87959c60

Subscribe to this mod's changes

spec-driven-dev is a skill published in the GitHub repository AmanKtyr/Tailor (3 stars, last pushed 9d ago), licensed MIT. It adds 35 tokens to every session and 1,173 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 2026-08-31.

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