writing-skills

writing-skills is a skill for Claude Code, Codex from JPM1118/Threadwork. It costs 43 tokens per session (1,235 once invoked), scanned A, original, MIT.

A guide for creating and editing coding-agent skills, which are reusable instructions for handling recurring tasks. It applies test-driven development, or TDD: test the instructions with realistic cases, then improve them when agents fail.

In plain words
What is it for?
Use it to design, revise, and verify skills by running pressure scenarios, checking agent behavior, and tightening the instructions.
Why use it?
It helps ensure a skill works in practice instead of merely sounding clear. Testing exposes gaps and loopholes before the skill is shared.

Skill for Claude CodeCodex

Part of the threadwork plugin — 20 skills, 4 commands, 1 agent, 1 hook shipped together

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/jpm1118/threadwork/writing-skills
Any agent
npx skills add JPM1118/Threadwork --skill writing-skills
Clone the repo
git clone --depth 1 https://github.com/JPM1118/Threadwork

Made for: Claude Code, Codex.

Or install threadwork, the plugin that ships this one along with the rest of its 20 skills, 4 commands, 1 agent, 1 hook.

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 writing-skills

README.md
[![agentmods](https://agentmods.dev/badge/skills/jpm1118/threadwork/writing-skills.svg)](https://agentmods.dev/skills/jpm1118/threadwork/writing-skills)
Your own site
<a href="https://agentmods.dev/skills/jpm1118/threadwork/writing-skills"><img src="https://agentmods.dev/badge/skills/jpm1118/threadwork/writing-skills.svg" alt="Measured on agentmods" height="20"></a>
Per session 43 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,235 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 5.1 $0.00043 $0.01235
Opus 5 $0.00022 $0.00617
Sonnet 5 $0.00009 $0.00247
Haiku 4.5 $0.00004 $0.00123

Measured 5d ago against content hash ae58d0a00e68, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

writing-skills 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/writing-skills/SKILL.md · 196 lines

How it starts

The opening of the file, as written. The whole thing — 196 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Writing Skills

Overview

Writing skills IS Test-Driven Development applied to process documentation.

You write test cases (pressure scenarios with subagents), watch them fail (baseline behavior), write the skill (documentation), watch tests pass (agents comply), and refactor (close loopholes).

Core principle: If you didn't watch an agent fail without the skill, you don't know if the skill teaches the right thing.

What is a Skill?

A skill is a reference guide for proven techniques, patterns, or tools. Skills help future Claude instances find and apply effective approaches.

Skills are: Reusable techniques, patterns, tools, reference guides

Skills are NOT: Narratives about how you solved a problem once

When to Create a Skill

Create when:

  • Technique wasn't intuitively obvious to you
  • You'd reference this again across projects
  • Pattern applies broadly (not project-specific)
  • Others would benefit

Don't create for:

  • One-off solutions
  • Standard practices well-documented elsewhere
  • Project-specific conventions (put in CLAUDE.md)

Skill Types

Type Description Examples
Technique Concrete method with steps condition-based-waiting, root-cause-tracing
Pattern Way of thinking about problems flatten-with-flags, test-invariants
Reference API docs, syntax guides office docs, tool references

Directory Structure

skills/
  skill-name/
    SKILL.md              # Main reference (required)
    supporting-file.*     # Only if needed

SKILL.md Structure

Frontmatter (YAML):

  • Only two fields: name and description
  • Max 1024 characters total
  • name: Use letters, numbers, and hyphens only
  • description: Third-person, includes WHAT and WHEN to use
---
name: skill-name-with-hyphens
description: Use when [triggers] - [what it does]
---

# Skill Name

## Overview
What is this? Core principle in 1-2 sentences.

## When to Use
Bullet list with SYMPTOMS and use cases
When NOT to use

## Core Pattern
Before/after code comparison

## Quick Reference
Table or bullets for scanning

## Common Mistakes
What goes wrong + fixes

Read the full file on GitHub · 196 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. 5d ago First seen · 196 lines · 43 tokens per session scan A ae58d0a00e68

Subscribe to this mod's changes

writing-skills is a skill published in the GitHub repository JPM1118/Threadwork (5 stars, last pushed 9mo ago), licensed MIT. It adds 43 tokens to every session and 1,235 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 2026-08-31.

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