spec

spec is a skill for Claude Code, Codex from Klerith/fernando-skills. It costs 42 tokens per session (2,786 once invoked), scanned A, original, MIT.

A guided method for writing a detailed software specification before coding. It helps clarify the goal, ask questions, and organize the plan into sections saved in a specs folder.

In plain words
What is it for?
Use it when starting a large feature or other substantial change that needs requirements, structure, and acceptance details defined before development.
Why use it?
It reduces ambiguity before implementation, so later code has a clear agreement to follow instead of relying on assumptions.

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/klerith/fernando-skills/spec
Any agent
npx skills add Klerith/fernando-skills --skill spec
Clone the repo
git clone --depth 1 https://github.com/Klerith/fernando-skills

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

README.md
[![agentmods](https://agentmods.dev/badge/skills/klerith/fernando-skills/spec.svg)](https://agentmods.dev/skills/klerith/fernando-skills/spec)
Your own site
<a href="https://agentmods.dev/skills/klerith/fernando-skills/spec"><img src="https://agentmods.dev/badge/skills/klerith/fernando-skills/spec.svg" alt="Measured on agentmods" height="20"></a>
Per session 42 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,786 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 $0.00042 $0.02786
Opus 5 $0.00021 $0.01393
Sonnet 5 $0.00008 $0.00557
Haiku 4.5 $0.00004 $0.00279

Measured 5d ago against content hash 9b2f92af0d80, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

spec 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 5d 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/engineering/spec/SKILL.md · 165 lines

How it starts

The opening of the file, as written. The whole thing — 165 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/spec — Guided spec designer

Session context

Today's date (use this for the spec header, never guess it): !date +%F

Specs that already exist: !ls specs/ 2>/dev/null || echo "The specs/ folder does not exist yet"


This skill helps you produce a useful spec following the spec-driven method. You don't write code here. Your job is to help the user clarify what they want to build, ask questions when something is not well-defined enough, and develop the spec section by section until it is ready to be saved into specs/.

Philosophy

A spec is not decorative documentation. It is the contract that drives later execution. If the spec is vague, the code will improvise. That is why this flow is deliberately slow during the definition phase and fast during the writing phase.

Read template.md (in the same directory as this skill) to see the full structure the spec will follow. Lean on it at every step.

Command flow

  • Follow the four phases in order. Never skip Phase 2 — the questions are the whole point. If the user wants to go faster, remind them that the cost of a bad spec gets paid later in code. (Phase 3 does have a fast path once Phase 2 is genuinely complete; see below.)
  • Your replies must be in the same language as the initial prompt. E.g.: if the initial prompt is in Spanish, your replies must be in Spanish; if it is in English, your replies must be in English.

Phase 1 — Understand the context

Before asking questions about the feature, make sure you have project context:

  1. Read the project-memory file, if one exists. Try in order and stop at the first hit: CLAUDE.md, AGENTS.md, GEMINI.md, README.md. This adapts the skill to whichever agent is running it (Claude Code, Codex, Gemini CLI, etc.).
  2. Look at the specs/ listing in the session context above to see which specs already exist and how they are numbered.
  3. If previous specs exist, read at least the two most recent ones to pick up the project's conventions — including the language they are written in and the exact wording they use for states and section headings. A new spec must match the existing ones.

Read the full file on GitHub · 165 lines

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. 5d ago First seen · 165 lines · 42 tokens per session scan A 9b2f92af0d80

Subscribe to this mod's changes

spec is a skill published in the GitHub repository Klerith/fernando-skills (213 stars, last pushed 1mo ago), licensed MIT. It adds 42 tokens to every session and 2,786 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 2026-08-30.

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