superpowers-writing-skills

superpowers-writing-skills is a skill for Claude Code, Codex from christopherarter/superpowers-reasonix. It costs 25 tokens per session (2,689 once invoked), scanned A, original, MIT.

A guide for creating, editing, and testing Reasonix skills, which are reusable instructions for an AI agent. It applies test-driven development (TDD)—checking failure cases before writing the instructions—to process documents.

In plain words
What is it for?
Use it to write test cases, check an agent’s baseline behaviour, create a skill, and refine its instructions.
Why use it?
It helps reveal whether a skill actually changes the agent’s behaviour and closes gaps before deployment.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions subagents; mentions AGENTS.md.

Good fit Use it to write test cases, check an agent’s baseline behaviour, create a skill, and refine its instructions.

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Install with agentmods
npx agentmods add skills/christopherarter/superpowers-reasonix/superpowers-writing-skills
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.

Any agent
npx skills add christopherarter/superpowers-reasonix --skill superpowers-writing-skills
Clone the repo
git clone --depth 1 https://github.com/christopherarter/superpowers-reasonix

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 superpowers-writing-skills

README.md
[![agentmods](https://agentmods.dev/badge/skills/christopherarter/superpowers-reasonix/superpowers-writing-skills/github.svg)](https://agentmods.dev/skills/christopherarter/superpowers-reasonix/superpowers-writing-skills)
Your own site
<a href="https://agentmods.dev/skills/christopherarter/superpowers-reasonix/superpowers-writing-skills"><img src="https://agentmods.dev/badge/skills/christopherarter/superpowers-reasonix/superpowers-writing-skills/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.

agentmods 80×15 button for superpowers-writing-skills

Your own site · 80×15
<a href="https://agentmods.dev/skills/christopherarter/superpowers-reasonix/superpowers-writing-skills"><img src="https://agentmods.dev/badge/skills/christopherarter/superpowers-reasonix/superpowers-writing-skills.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 25 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,689 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. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Rogue Agent · line 10
    Skill modifies its own code, configuration, or behavior at runtime. Self-modification enables an agent to escalate privileges, disable safety constraints, or install persistent backdoors.
    Fix: Prevent the skill from modifying its own code, SKILL.md, or configuration files. Treat skill files as read-only at runtime.
How audits are shown
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 $0.00025 $0.02689
Opus 5 $0.00013 $0.01345
Sonnet 5 $0.00005 $0.00538
Haiku 4.5 $0.00003 $0.00269

Measured 11d ago against content hash c7d98818e23f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

superpowers-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 11d 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/superpowers-writing-skills/SKILL.md · 166 lines

How it starts

The opening of the file, as written. The whole thing — 166 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Writing Skills (for Reasonix)

Overview

Writing skills IS TDD for process docs. Write test cases (pressure scenarios, subagents). Watch fail (baseline). Write skill. Watch pass (agent complies). Refactor (close loopholes).

Core principle: Didn't watch an agent fail without the skill? Don't know it teaches the right thing.

REQUIRED BACKGROUND: Know superpowers-test-driven-development first — defines RED-GREEN-REFACTOR. This adapts it to docs.

Platform spec: Full Reasonix skill/hook/MCP contract → extending-reasonix. This = authoring discipline; that = exhaustive spec.

What is a Skill?

Reusable playbook the model invokes via run_skill / read_skill (user: /name). Two kinds:

  • Inline — body folds into the turn as a tool result. Default.
  • Subagent (runAs: subagent) — body = a child's system prompt; runs isolated, returns only its final answer. Use only when work is context-heavy and only the conclusion matters.

ARE: reusable techniques, patterns, tools, reference guides. NOT: narratives of solving something once.

Reasonix Skill Anatomy (get these right)

Where skills live & how found

  • Discovery roots, highest priority first: project {.reasonix,.agents,.agent,.claude}/skills/[skills] paths in reasonix.toml → home ~/{.reasonix,...}/skills/ → built-ins.
  • First match by name wins (user review overrides built-in). Layout: <root>/skills/<name>/SKILL.md; flat <name>.md works too.

Name

Regex: ^[a-zA-Z0-9][a-zA-Z0-9._-]{0,63}$ — letters/digits/./_/-, ≤64 chars, alphanumeric start. Frontmatter name: overrides the dir stem.

Frontmatter — Reasonix's OWN minimal parser, not real YAML

  • --- opens, next --- closes. Unclosed fence → WHOLE file is the body (no frontmatter). Always close it.
  • Lines = key: value. Keys lowercased (runAs=runas). Values trimmed of one quote layer. Empty value + - item lines = list (comma-joined), so allowed-tools can be a YAML list.
  • No block scalars (>/|), no multi-line values, no nesting. One line per value.

Read the full file on GitHub · 166 lines

Files

What ships with it

1 file 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. 11d ago First seen · 166 lines · 25 tokens per session scan A c7d98818e23f

Subscribe to this mod's changes

superpowers-writing-skills is a skill published in the GitHub repository christopherarter/superpowers-reasonix (99 stars, last pushed 21d ago), licensed MIT. It adds 25 tokens to every session and 2,689 once invoked, about $0.0001 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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