skill-writer

A guide for creating and maintaining Agent Skills, which are instruction packages that teach AI agents how to handle specific kinds of work.

In plain words
What is it for?
Use it to plan a skill's scope, write or update its SKILL.md file, set its metadata, and check its structure.
Why use it?
It helps avoid unclear instructions, invalid files, and discovery problems when building or changing a skill.

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/lessweb/deepcode-cli/skill-writer
Any agent
npx skills add lessweb/deepcode-cli --skill skill-writer
Clone the repo
git clone --depth 1 https://github.com/lessweb/deepcode-cli

Made for: Claude Code, Codex.

Per session 59 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,229 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 $0.00059 $0.02229
Opus 5 $0.00030 $0.01115
Sonnet 5 $0.00012 $0.00446
Haiku 4.5 $0.00006 $0.00223

Measured yesterday against content hash 05cd9502973f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

skill-writer 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.

packages/core/templates/skills/bundled/skill-writer/SKILL.md · 403 lines

How it starts

The opening of the file, as written. The whole thing — 403 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Skill Writer

This Skill helps you create well-structured Agent Skills for AI agents that follow best practices and validation requirements.

When to use this Skill

Use this Skill when:

  • Creating a new Agent Skill
  • Writing or updating SKILL.md files
  • Designing skill structure and frontmatter
  • Troubleshooting skill discovery issues
  • Converting existing prompts or workflows into Skills

Instructions

Step 1: Determine Skill scope

First, understand what the Skill should do:

  1. Ask clarifying questions:

    • What specific capability should this Skill provide?
    • When should AI agents use this Skill?
    • What tools or resources does it need?
    • Is this for personal use or team sharing?
  2. Keep it focused: One Skill = one capability

    • Good: "PDF form filling", "Excel data analysis"
    • Too broad: "Document processing", "Data tools"

Step 2: Choose Skill location

Determine where to create the Skill:

Personal Skills (~/.agents/skills/):

  • Individual workflows and preferences
  • Experimental Skills
  • Personal productivity tools

Project Skills (.agents/skills/):

  • Team workflows and conventions
  • Project-specific expertise
  • Shared utilities (committed to git)

Step 3: Create Skill structure

Create the directory and files:

# Personal
mkdir -p ~/.agents/skills/skill-name

# Project
mkdir -p .agents/skills/skill-name

For multi-file Skills:

skill-name/
├── SKILL.md (required)
├── reference.md (optional)
├── examples.md (optional)
├── scripts/
│   └── helper.py (optional)
└── templates/
    └── template.txt (optional)

Step 4: Write SKILL.md frontmatter

Create YAML frontmatter with required fields:

---
name: skill-name
description: Brief description of what this does and when to use it
---

Field requirements:

  • name:
    • Lowercase letters, numbers, hyphens only
    • Max 64 characters
    • Must match directory name
    • Good: pdf-processor, git-commit-helper
    • Bad: PDF_Processor, Git Commits!

Read the full file on GitHub · 403 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. yesterday First seen · 403 lines · 59 tokens per session scan A 05cd9502973f

Subscribe to this mod's changes

skill-writer is a skill published in the GitHub repository lessweb/deepcode-cli (2,224 stars, last pushed 4d ago), licensed MIT. It adds 59 tokens to every session and 2,229 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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