spec-writer

spec-writer is an agent for coding agents from MadAppGang/claude-code. It costs 31 tokens per session (1,121 once invoked), scanned A, original, MIT.

A specification-writing agent that turns interview notes, project context, and collected assets into a structured product specification and task list.

In plain words
What is it for?
Use it to produce functional requirements, user stories, acceptance criteria, non-functional requirements, and an implementation breakdown.
Why use it?
It helps convert conversations and scattered technical information into requirements that developers can implement and verify.

Agent

Part of the dev plugin — 47 skills, 12 commands, 14 agents 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 agents/madappgang/claude-code/spec-writer
Clone the repo
git clone --depth 1 https://github.com/MadAppGang/claude-code

Or install dev, the plugin that ships this one along with the rest of its 47 skills, 12 commands, 14 agents.

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-writer

README.md
[![agentmods](https://agentmods.dev/badge/agents/madappgang/claude-code/spec-writer.svg)](https://agentmods.dev/agents/madappgang/claude-code/spec-writer)
Your own site
<a href="https://agentmods.dev/agents/madappgang/claude-code/spec-writer"><img src="https://agentmods.dev/badge/agents/madappgang/claude-code/spec-writer.svg" alt="Measured on agentmods" height="20"></a>
Per session 31 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 1,121 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 $0.00031 $0.01121
Opus 5 $0.00015 $0.00561
Sonnet 5 $0.00006 $0.00224
Haiku 4.5 $0.00003 $0.00112

Measured yesterday against content hash af7a1e8f9e13, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

spec-writer 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 yesterday.

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.

plugins/dev/agents/spec-writer.md · 183 lines

How it starts

The opening of the file, as written. The whole thing — 183 lines — stays where its author put it; the contents beside it link to each section on GitHub.

<input_files>
  Required inputs in ${SESSION_PATH}/:
  - interview-log.md (complete Q&A history)
  - assets.md (collected API specs, Figma links, etc.)
  - context.json (detected stack, project info)

  Optional inputs:
  - existing-spec.md (if started from existing spec)
  - focus-areas.md (coverage tracking)
</input_files>

<output_files>
  Outputs to ${SESSION_PATH}/:
  - spec.md (comprehensive specification)
  - tasks.md (implementation task breakdown)
</output_files>

</critical_constraints>

<spec_structure> Generate spec.md with this structure: ```markdown # Specification: {Project/Feature Name}

## Executive Summary
{2-3 sentence overview synthesized from interview}

## Functional Requirements

### Core Features
{Extracted from interview, prioritized}

### User Stories
{In "As a X, I want Y, so that Z" format}

### Acceptance Criteria
{Testable criteria for each feature}

## Non-Functional Requirements

### Performance
- Response times: {from interview}
- Throughput: {from interview}
- Concurrent users: {from interview}

### Security
{Authentication, authorization, compliance from interview}

### Scalability
{Scale requirements from interview}

## Technical Specifications

### Technology Stack
{From context.json and interview}

### API Contracts
{From assets.md or synthesized from interview}

### Data Models
{Key entities discussed in interview}

## User Experience

### User Flows
{Critical paths from interview}

### UI Requirements
{Design system, components, accessibility}

## Edge Cases & Error Handling
{From interview edge case questions}

## Integration Points
{External APIs, third-party services}

## Constraints
{Technical, business, regulatory from interview}

## Trade-offs Discussed
| Decision | Options | Chosen | Rationale |
|----------|---------|--------|-----------|

## Open Questions
{Any unresolved items from interview}

## Success Criteria
{How we know this is complete}

---
*Generated from interview session: {SESSION_ID}*
*Interview rounds: {N}*
```

</spec_structure>

<tasks_structure> Generate tasks.md with this structure: ```markdown # Implementation Tasks

## Phase 1: Foundation
- [ ] Task 1: {description} [S/M/L]
- [ ] Task 2: {description} [S/M/L]

## Phase 2: Core Features
- [ ] Task 3: {description} [S/M/L]

## Phase 3: Integration
- [ ] Task 4: {description} [S/M/L]

## Phase 4: Polish
- [ ] Task 5: {description} [S/M/L]

## Dependencies
- Task 3 depends on Task 1, 2
- Task 4 depends on Task 3

## Suggested Order
1. {recommended starting point}
2. {next steps}

---
*Ready for: /dev:feature {feature_name}*
```

</tasks_structure>

  Synthesize specification from interview session.
</request>
<action>
  1. Read interview-log.md (6 rounds of Q&A)
  2. Read assets.md (Figma link, OpenAPI spec)
  3. Read context.json (React + Bun stack)
  4. Synthesize spec.md with all sections
  5. Create tasks.md with 12 implementation tasks
  6. Return: "Spec synthesized: 12 requirements, 8 user stories, 12 tasks"
</action>

Read the full file on GitHub · 183 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. yesterday First seen · 183 lines · 31 tokens per session scan A af7a1e8f9e13

Subscribe to this mod's changes

spec-writer is an agent published in the GitHub repository MadAppGang/claude-code (279 stars, last pushed 5mo ago), licensed MIT. It adds 31 tokens to every session and 1,121 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.