spec-writing

spec-writing is a skill for Codex from itseffi/agentic-os. It costs 26 tokens per session (396 once invoked), scanned A, original, MIT.

A technical plan that turns an approved product requirements document or clear requirements into instructions developers can implement. It defines the scope, connections between parts, and conditions for acceptance.

In plain words
What is it for?
Use it to prepare implementation plans for features, services, APIs, or other engineering work.
Why use it?
It removes guesswork between product decisions and code changes. Developers can use one shared description of what to build and how to tell when it is complete.

Skill for Codex

Written for Codex: agents/openai.yaml present. Also seen: installed under .agents/ (shared by several agents).

Good fit Use it to prepare implementation plans for features, services, APIs, or other engineering work.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/itseffi/agentic-os/spec-writing
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 itseffi/agentic-os --skill spec-writing
Clone the repo
git clone --depth 1 https://github.com/itseffi/agentic-os

Made for: 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-writing

README.md
[![agentmods](https://agentmods.dev/badge/skills/itseffi/agentic-os/spec-writing/github.svg)](https://agentmods.dev/skills/itseffi/agentic-os/spec-writing)
Your own site
<a href="https://agentmods.dev/skills/itseffi/agentic-os/spec-writing"><img src="https://agentmods.dev/badge/skills/itseffi/agentic-os/spec-writing/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.

agentmods 80×15 button for spec-writing

Your own site · 80×15
<a href="https://agentmods.dev/skills/itseffi/agentic-os/spec-writing"><img src="https://agentmods.dev/badge/skills/itseffi/agentic-os/spec-writing.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 396 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00026 $0.00396
Opus 5.5 $0.00010 $0.00158
Sonnet 5.5 $0.00005 $0.00079
Haiku 4.5 $0.00003 $0.00040

Measured 1mo ago against content hash 91a3362933f0, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

spec-writing 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 1mo 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.

.agents/skills/spec-writing/SKILL.md · 94 lines

What it actually says

Spec Writing

Use this skill to produce an implementation-ready spec before planning or coding.

The Process

Step 1: Validate inputs

Require one of:

  • approved PRD
  • clear requirements with goals and constraints

If inputs are missing or ambiguous, list assumptions and open questions first.

Step 2: Define scope boundaries

Document:

  • in scope
  • out of scope
  • constraints (time, dependencies, compliance, platform)

Step 3: Define solution design

Specify:

  • architecture overview (high-level components)
  • interfaces/contracts
  • data model changes
  • rollout and migration approach

Step 4: Define acceptance and verification

Include:

  • acceptance criteria (testable)
  • non-functional expectations (performance, security, reliability)
  • verification commands/checks required before completion

Output Format

# [Feature Name] Technical Spec

## Goal
[What this spec delivers and why]

## Scope
- In scope:
- Out of scope:
- Constraints:

## Design
- Architecture:
- Interfaces/contracts:
- Data model changes:
- Migration/rollout:

## Risks and Dependencies
- Risks:
- Dependencies:
- Mitigations:

## Acceptance Criteria
- AC1:
- AC2:
- AC3:

## Verification Plan
- Required checks:
- Commands:
- Evidence to capture:

## Open Questions
- Q1:
- Q2:

Quality Bar

  • No vague placeholders in final output
  • Acceptance criteria must be measurable
  • Verification plan must include explicit commands

When to Use

Use this skill when the task directly matches the workflow described above.

When Not to Use

Do not use this skill when the request is unrelated, low-stakes, or better handled by a simpler direct response.

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 1mo ago First seen · 94 lines · 26 tokens per session scan A 91a3362933f0

Subscribe to this mod's changes

spec-writing is a skill published in the GitHub repository itseffi/agentic-os (117 stars, last pushed 15d ago), licensed MIT. It adds 26 tokens to every session and 396 once invoked, about $0.0001 per session on Opus 5.5. 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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