spec-impl

spec-impl is a skill for Claude Code, Codex from Klerith/fernando-skills. It costs 51 tokens per session (2,595 once invoked), scanned A, original, MIT.

A workflow for implementing an approved software specification, including finding the specification, creating a matching Git branch, and applying the changes step by step.

In plain words
What is it for?
Use it to select a specification, verify its approval status, create the required branch, implement the plan in phases, and pause for diff review.
Why use it?
It ensures implementation starts only after approval and keeps the work separated in a branch for review.

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-impl
Any agent
npx skills add Klerith/fernando-skills --skill spec-impl
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-impl

README.md
[![agentmods](https://agentmods.dev/badge/skills/klerith/fernando-skills/spec-impl.svg)](https://agentmods.dev/skills/klerith/fernando-skills/spec-impl)
Your own site
<a href="https://agentmods.dev/skills/klerith/fernando-skills/spec-impl"><img src="https://agentmods.dev/badge/skills/klerith/fernando-skills/spec-impl.svg" alt="Measured on agentmods" height="20"></a>
Per session 51 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,595 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 $0.00051 $0.02595
Opus 5 $0.00026 $0.01298
Sonnet 5 $0.00010 $0.00519
Haiku 4.5 $0.00005 $0.00260

Measured 4d ago against content hash 4a998e9a34ad, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

spec-impl 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 4d 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-impl/SKILL.md · 236 lines

How it starts

The opening of the file, as written. The whole thing — 236 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/spec-impl — Implementer of approved specs

Session context

Current repository state: !git status --short

Current branch: !git branch --show-current

Specs available in this folder: !ls specs/ 2>/dev/null || echo "The specs/ folder does not exist"

Branch-creation config: !cat specs/.spec-config.yml 2>/dev/null || echo "AutoCreateBranch: true (default, no config file)"


Instructions

Follow these four phases in strict order. Do not advance to the next phase if the previous one did not complete correctly.


Phase 1 — Identify the spec

The received argument is: $ARGUMENTS

If $ARGUMENTS is empty:

  • List the files available in specs/ (you already have them above).
  • Ask the user to specify the exact name of the spec.
  • Stop and wait for an answer. Do not continue.

If $ARGUMENTS has a value:

  • Look for the file in specs/. The user may have written the full name (01-mvp-arkanoid), only the number (01), or only the slug (mvp-arkanoid). Try to find the correct file in any of those cases.
  • If you do not find the file, show the available specs and ask the user to correct the name.
  • If you do find it, continue to Phase 2.

Phase 2 — Validate the spec's state

Read the spec file you located in Phase 1 using the Read tool or cat.

In the file's contents, look for the line that contains the spec's state. The header label is typically **Status:** (English) or **Estado:** (Spanish), but it may use any language. Match by position (status line near the top of the spec) and by the surrounding state machine, not by the exact label.

Absolute rule: You can only continue if the state means "Approved" — regardless of the language used.

Treat any of the following (and their equivalents in other languages) as the Approved state and continue:

  • English: Approved
  • Spanish: Aprobado
  • Portuguese: Aprovado
  • French: Approuvé
  • German: Genehmigt
  • Italian: Approvato
  • …or any other language's word that clearly means "approved"

Read the full file on GitHub · 236 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. 4d ago First seen · 236 lines · 51 tokens per session scan A 4a998e9a34ad

Subscribe to this mod's changes

spec-impl is a skill published in the GitHub repository Klerith/fernando-skills (213 stars, last pushed 1mo ago), licensed MIT. It adds 51 tokens to every session and 2,595 once invoked, about $0.0003 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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