skill-building

A guide to creating skills for Claude Code, including the SKILL.md file structure and ways to organize instructions so details are shown when needed.

In plain words
What is it for?
It is for building skills, writing or improving SKILL.md files, refining descriptions, and planning skill instructions.
Why use it?
It helps avoid unclear or poorly structured skill instructions.

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/anexileddev/codeforge/skill-building
Any agent
npx skills add AnExiledDev/CodeForge --skill skill-building
Clone the repo
git clone --depth 1 https://github.com/AnExiledDev/CodeForge

Made for: Claude Code, Codex.

Per session 89 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,306 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown 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 $0.00089 $0.02306
Opus 5 $0.00044 $0.01153
Sonnet 5 $0.00018 $0.00461
Haiku 4.5 $0.00009 $0.00231

Measured yesterday against content hash 093366fb785f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

skill-building 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.

container/.devcontainer/plugins/devs-marketplace/plugins/skill-engine/skills/skill-building/SKILL.md · 222 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

Files

What ships with it

3 files 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. yesterday First seen · 222 lines · 89 tokens per session scan A 093366fb785f

Subscribe to this mod's changes

skill-building is a skill published in the GitHub repository AnExiledDev/CodeForge (9 stars, last pushed 1mo ago), with no licence file. It adds 89 tokens to every session and 2,306 once invoked, about $0.0004 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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