What is skill-authoring?

A guide for writing reusable instructions for coding agents, stored in a file named SKILL.md. It covers how to structure, test, improve, and publish those instructions.

Use it to create or revise an agent skill, define its triggers and exclusions, add supporting references or scripts, verify its quality, or publish it to a repository.

It helps turn specialist knowledge or a repeatable workflow into instructions an agent can apply when the right task appears. It also addresses the details that determine when an agent should activate the skill.

skill-authoring — Skill for Claude Code and Codex by majdghithan

Install

Getting it into your agent

There is no command for this one: it runs only inside a plugin, and the catalogue could not identify which plugin ships it. The source is linked below.

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/majdghithan/agent-skills/skill-authoring/github.svg)](https://agentmods.dev/skills/majdghithan/agent-skills/skill-authoring)

Your own site

<a href="https://agentmods.dev/skills/majdghithan/agent-skills/skill-authoring"><img src="https://agentmods.dev/badge/skills/majdghithan/agent-skills/skill-authoring/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/majdghithan/agent-skills/skill-authoring"><img src="https://agentmods.dev/badge/skills/majdghithan/agent-skills/skill-authoring.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 101 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,367 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.

Model	Per session	Once invoked
Fable 5.1	$0.00101	$0.01367
Opus 5	$0.00051	$0.00683
Sonnet 5	$0.00020	$0.00273
Haiku 4.5	$0.00010	$0.00137

Measured 9d ago against content hash 9ce08e82a245, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

skill-authoring 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 9d 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/skill-authoring/SKILL.md · 75 lines

How it starts

The opening of the file, as written. The whole thing — 75 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill authoring - write a great, publishable skill

A skill is a SKILL.md file (YAML frontmatter + markdown instructions) that an agent loads when its work matches. Optionally it bundles supporting files (references/*.md, scripts/) loaded on demand. Good skills are specific, accurate, and lean. This skill is how to write one.

1. Decide it should exist

Write a skill when there's real, reusable know-how an agent would otherwise get wrong or generic: a framework's version-specific rules, a migration's gotchas, a self-hosting workflow, a house style. Don't write one for a one-off task, or for something the model already does well. Check the ecosystem first (npx skills find <topic>) - if a great one exists, install it instead; if only generic ones exist, that's your gap.

2. Frontmatter - name + description (the description is critical)

---
name: kebab-case-name          # matches the folder name
description: <what it does> + <when to use it> + <trigger phrases> + <when NOT to use>
---

The description is how the agent decides to activate the skill - spend real effort on it. Pack it with concrete trigger phrases the user might say, the situations it covers, and an explicit "use when… / do not use for…" boundary. A vague description means the skill never fires (or fires wrongly).

3. Structure - lean SKILL.md, detail in references (progressive disclosure)

Keep SKILL.md short and scannable. It's loaded every time the skill activates - don't bloat the context. Put the always-true guidance here; push deep or bulky detail into references/<topic>.md that the agent reads only when needed.
When the topic has variants (versions, dialects, platforms), lead with a "detect first" step, then route to the matching reference. Example: a framework skill opens by reading composer.json/package.json to find the installed major version, then loads references/<name>-vN.md. This is what keeps a skill correct as the tool evolves.
Separate the stable layer from the volatile layer. Version-independent principles live in SKILL.md; exact namespaces/signatures live in per-version references (and say "verify against the official docs for this version" rather than freezing volatile API).

Layout for a multi-file skill:

skills/<name>/
  SKILL.md                 # detect + route + stable principles
  references/<topic>.md     # loaded on demand
  references/upgrades/*.md   # e.g. migration/upgrade paths

Read the full file on GitHub · 75 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.

9d ago First seen · 75 lines · 101 tokens per session scan A 9ce08e82a245

Subscribe to this mod's changes

skill-authoring is a skill published in the GitHub repository majdghithan/agent-skills (7 stars, last pushed 1mo ago), licensed MIT. It adds 101 tokens to every session and 1,367 once invoked, about $0.0005 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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