writing-skills

$2b

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

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

TDD Mapping for Skills

TDD Concept

Skill Creation

Test case

Pressure scenario with subagent

Production code

Skill document (SKILL.md)

Test fails (RED)

Agent violates rule without skill (baseline)

Test passes (GREEN)

Agent complies with skill present

Refactor

Close loopholes while maintaining compliance

Write test first

Run baseline scenario BEFORE writing skill

Watch it fail

Document exact rationalizations agent uses

Minimal code

Write skill addressing those specific violations

Watch it pass

Verify agent now complies

Refactor cycle

Find new rationalizations → plug → re-verify

The entire skill creation process follows RED-GREEN-REFACTOR.

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)

• Mechanical constraints (if it's enforceable with regex/validation, automate it—save documentation for judgment calls)

Skill Types

Technique

Concrete method with steps to follow (condition-based-waiting, root-cause-tracing)

Pattern

Way of thinking about problems (flatten-with-flags, test-invariants)

Reference

API docs, syntax guides, tool documentation (office docs)

Directory Structure

skills/

  skill-name/

    SKILL.md              # Main reference (required)

    supporting-file.*     # Only if needed

Flat namespace - all skills in one searchable namespace

Separate files for:

• Heavy reference (100+ lines) - API docs, comprehensive syntax

• Reusable tools - Scripts, utilities, templates

Keep inline:

• Principles and concepts

• Code patterns (< 50 lines)

• Everything else

SKILL.md Structure

Frontmatter (YAML):

• Two required fields: name and description (see agentskills.io/specification for all supported fields)

• Max 1024 characters total

• name: Use letters, numbers, and hyphens only (no parentheses, special chars)

• description: Third-person, describes ONLY when to use (NOT what it does)

• Start with "Use when..." to focus on triggering conditions

• Include specific symptoms, situations, and contexts

• NEVER summarize the skill's process or workflow (see CSO section for why)

• Keep under 500 characters if possible

---

name: Skill-Name-With-Hyphens

description: Use when [specific triggering conditions and symptoms]

---

# Skill Name

## Overview

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

## When to Use

[Small inline flowchart IF decision non-obvious]

Bullet list with SYMPTOMS and use cases

When NOT to use

## Core Pattern (for techniques/patterns)

Before/after code comparison

## Quick Reference

Table or bullets for scanning common operations

## Implementation

Inline code for simple patterns

Link to file for heavy reference or reusable tools

## Common Mistakes

What goes wrong + fixes

## Real-World Impact (optional)

Concrete results

Claude Search Optimization (CSO)

Critical for discovery: Future Claude needs to FIND your skill

1. Rich Description Field

Purpose: Claude reads description to decide which skills to load for a given task. Make it answer: "Should I read this skill right now?"

Format: Start with "Use when..." to focus on triggering conditions

CRITICAL: Description = When to Use, NOT What the Skill Does

The description should ONLY describe triggering conditions. Do NOT summarize the skill's process or workflow in the description.

Why this matters: Testing revealed that when a description summarizes the skill's workflow, Claude may follow the description instead of reading the full skill content. A description saying "code review between tasks" caused Claude to do ONE review, even though the skill's flowchart clearly showed TWO reviews (spec compliance then code quality).

When the description was changed to just "Use when executing implementation plans with independent tasks" (no workflow summary), Claude correctly read the flowchart and followed the two-stage review process.

The trap: Descriptions that summarize workflow create a shortcut Claude will take. The skill body becomes documentation Claude skips.

# ❌ BAD: Summarizes workflow - Claude may follow this instead of reading skill

description: Use when executing plans - dispatches subagent per task with code review between tasks

# ❌ BAD: Too much process detail

description: Use for TDD - write test first, watch it fail, write minimal code, refactor

# ✅ GOOD: Just triggering conditions, no workflow summary

description: Use when executing implementation plans with independent tasks in the current session

# ✅ GOOD: Triggering conditions only

description: Use when implementing any feature or bugfix, before writing implementation code

Content:

• Use concrete triggers, symptoms, and situations that signal this skill applies

• Describe the problem (race conditions, inconsistent behavior) not language-specific symptoms (setTimeout, sleep)

• Keep triggers technology-agnostic unless the skill itself is technology-specific

• If skill is technology-specific, make that explicit in the trigger

• Write in third person (injected into system prompt)

• NEVER summarize the skill's process or workflow

# ❌ BAD: Too abstract, vague, doesn't include when to use

description: For async testing

# ❌ BAD: First person

description: I can help you with async tests when they're flaky

# ❌ BAD: Mentions technology but skill isn't specific to it

description: Use when tests use setTimeout/sleep and are flaky

# ✅ GOOD: Starts with "Use when", describes problem, no workflow

description: Use when tests have race conditions, timing dependencies, or pass/fail inconsistently

# ✅ GOOD: Technology-specific skill with explicit trigger

description: Use when using React Router and handling authentication redirects

2. Keyword Coverage

Use words Claude would search for:

• Error messages: "Hook timed out", "ENOTEMPTY", "race condition"

• Symptoms: "flaky", "hanging", "zombie", "pollution"

• Synonyms: "timeout/hang/freeze", "cleanup/teardown/afterEach"

• Tools: Actual commands, library names, file types

3. Descriptive Naming

Use active voice, verb-first:

• ✅ creating-skills not skill-creation

• ✅ condition-based-waiting not async-test-helpers

4. Token Efficiency (Critical)

Problem: getting-started and frequently-referenced skills load into EVERY conversation. Every token counts.

Target word counts:

• getting-started workflows: <150 words each

• Frequently-loaded skills: <200 words total

• Other skills: <500 words (still be concise)

Techniques:

Move details to tool help:

# ❌ BAD: Document all flags in SKILL.md

search-conversations supports --text, --both, --after DATE, --before DATE, --limit N

# ✅ GOOD: Reference --help

search-conversations supports multiple modes and filters. Run --help for details.

Use cross-references:

# ❌ BAD: Repeat workflow details

When searching, dispatch subagent with template...

[20 lines of repeated instructions]

# ✅ GOOD: Reference other skill

Always use subagents (50-100x context savings). REQUIRED: Use [other-skill-name] for workflow.

Compress examples:

# ❌ BAD: Verbose example (42 words)

your human partner: "How did we handle authentication errors in React Router before?"

You: I'll search past conversations for React Router authentication patterns.

[Dispatch subagent with search query: "React Router authentication error handling 401"]

# ✅ GOOD: Minimal example (20 words)

Partner: "How did we handle auth errors in React Router?"

You: Searching...

[Dispatch subagent → synthesis]

Eliminate redundancy:

• Don't repeat what's in cross-referenced skills

• Don't explain what's obvious from command

• Don't include multiple examples of same pattern

Verification:

wc -w skills/path/SKILL.md

# getting-started workflows: aim for <150 each

# Other frequently-loaded: aim for <200 total

Name by what you DO or core insight:

• ✅ condition-based-waiting > async-test-helpers

• ✅ using-skills not skill-usage

• ✅ flatten-with-flags > data-structure-refactoring

• ✅ root-cause-tracing > debugging-techniques

Gerunds (-ing) work well for processes:

• creating-skills, testing-skills, debugging-with-logs

• Active, describes the action you're taking

4. Cross-Referencing Other Skills

When writing documentation that references other skills:

Use skill name only, with explicit requirement markers:

• ✅ Good: **REQUIRED SUB-SKILL:** Use superpowers:test-driven-development

• ✅ Good: **REQUIRED BACKGROUND:** You MUST understand superpowers:systematic-debugging

• ❌ Bad: See skills/testing/test-driven-development (unclear if required)

• ❌ Bad: @skills/testing/test-driven-development/SKILL.md (force-loads, burns context)

Why no @ links: @ syntax force-loads files immediately, consuming 200k+ context before you need them.

Flowchart Usage

digraph when_flowchart {

    "Need to show information?" [shape=diamond];

    "Decision where I might go wrong?" [shape=diamond];

    "Use markdown" [shape=box];

    "Small inline flowchart" [shape=box];

    "Need to show information?" -> "Decision where I might go wrong?" [label="yes"];

    "Decision where I might go wrong?" -> "Small inline flowchart" [label="yes"];

    "Decision where I might go wrong?" -> "Use markdown" [label="no"];

}

Use flowcharts ONLY for:

• Non-obvious decision points

• Process loops where you might stop too early

• "When to use A vs B" decisions

Never use flowcharts for:

• Reference material → Tables, lists

• Code examples → Markdown blocks

• Linear instructions → Numbered lists

• Labels without semantic meaning (step1, helper2)

See @graphviz-conventions.dot for graphviz style rules.

Visualizing for your human partner: Use render-graphs.js in this directory to render a skill's flowcharts to SVG:

./render-graphs.js ../some-skill           # Each diagram separately

./render-graphs.js ../some-skill --combine # All diagrams in one SVG

Code Examples

One excellent example beats many mediocre ones

Choose most relevant language:

• Testing techniques → TypeScript/JavaScript

• System debugging → Shell/Python

• Data processing → Python

Good example:

• Complete and runnable

• Well-commented explaining WHY

• From real scenario

• Shows pattern clearly

• Ready to adapt (not generic template)

Don't:

• Implement in 5+ languages

• Create fill-in-the-blank templates

• Write contrived examples

You're good at porting - one great example is enough.

File Organization

Self-Contained Skill

defense-in-depth/

  SKILL.md    # Everything inline

When: All content fits, no heavy reference needed

Skill with Reusable Tool

condition-based-waiting/

  SKILL.md    # Overview + patterns

  example.ts  # Working helpers to adapt

When: Tool is reusable code, not just narrative

Skill with Heavy Reference

pptx/

  SKILL.md       # Overview + workflows

  pptxgenjs.md   # 600 lines API reference

  ooxml.md       # 500 lines XML structure

  scripts/       # Executable tools

When: Reference material too large for inline

The Iron Law (Same as TDD)

NO SKILL WITHOUT A FAILING TEST FIRST

This applies to NEW skills AND EDITS to existing skills.

Write skill before testing? Delete it. Start over.

Edit skill without testing? Same violation.

No exceptions:

• Not for "simple additions"

• Not for "just adding a section"

• Not for "documentation updates"

• Don't keep untested changes as "reference"

• Don't "adapt" while running tests

• Delete means delete

REQUIRED BACKGROUND: The superpowers:test-driven-development skill explains why this matters. Same principles apply to documentation.

Testing All Skill Types

Different skill types need different test approaches:

Discipline-Enforcing Skills (rules/requirements)

Examples: TDD, verification-before-completion, designing-before-coding

Test with:

• Academic questions: Do they understand the rules?

• Pressure scenarios: Do they comply under stress?

• Multiple pressures combined: time + sunk cost + exhaustion

• Identify rationalizations and add explicit counters

Success criteria: Agent follows rule under maximum pressure

Technique Skills (how-to guides)

Examples: condition-based-waiting, root-cause-tracing, defensive-programming

Test with:

• Application scenarios: Can they apply the technique correctly?

• Variation scenarios: Do they handle edge cases?

• Missing information tests: Do instructions have gaps?

Success criteria: Agent successfully applies technique to new scenario

Pattern Skills (mental models)

Examples: reducing-complexity, information-hiding concepts

Test with:

• Recognition scenarios: Do they recognize when pattern applies?

• Application scenarios: Can they use the mental model?

• Counter-examples: Do they know when NOT to apply?

Success criteria: Agent correctly identifies when/how to apply pattern

Reference Skills (documentation/APIs)

Examples: API documentation, command references, library guides

Test with:

• Retrieval scenarios: Can they find the right information?

• Application scenarios: Can they use what they found correctly?

• Gap testing: Are common use cases covered?

Success criteria: Agent finds and correctly applies reference information

Common Rationalizations for Skipping Testing

Excuse

Reality

"Skill is obviously clear"

Clear to you ≠ clear to other agents. Test it.

"It's just a reference"

References can have gaps, unclear sections. Test retrieval.

"Testing is overkill"

Untested skills have issues. Always. 15 min testing saves hours.

"I'll test if problems emerge"

Problems = agents can't use skill. Test BEFORE deploying.

"Too tedious to test"

Testing is less tedious than debugging bad skill in production.

"I'm confident it's good"

Overconfidence guarantees issues. Test anyway.

"Academic review is enough"

Reading ≠ using. Test application scenarios.

"No time to test"

Deploying untested skill wastes more time fixing it later.

All of these mean: Test before deploying. No exceptions.

Bulletproofing Skills Against Rationalization

Skills that enforce discipline (like TDD) need to resist rationalization. Agents are smart and will find loopholes when under pressure.

Psychology note: Understanding WHY persuasion techniques work helps you apply them systematically. See persuasion-principles.md for research foundation (Cialdini, 2021; Meincke et al., 2025) on authority, commitment, scarcity, social proof, and unity principles.

Close Every Loophole Explicitly

Don't just state the rule - forbid specific workarounds:

No exceptions:

• Don't keep it as "reference"

• Don't "adapt" it while writing tests

• Don't look at it

• Delete means delete

</Good>

### Address "Spirit vs Letter" Arguments

Add foundational principle early:

Violating the letter of the rules is violating the spirit of the rules.

This cuts off entire class of "I'm following the spirit" rationalizations.

### Build Rationalization Table

Capture rationalizations from baseline testing (see Testing section below). Every excuse agents make goes in the table:

### Create Red Flags List

Make it easy for agents to self-check when rationalizing:

Red Flags - STOP and Start Over

• Code before test

• "I already manually tested it"

• "Tests after achieve the same purpose"

• "It's about spirit not ritual"

• "This is different because..."

All of these mean: Delete code. Start over with TDD.

### Update CSO for Violation Symptoms

Add to description: symptoms of when you're ABOUT to violate the rule:

description: use when implementing any feature or bugfix, before writing implementation code

## RED-GREEN-REFACTOR for Skills

Follow the TDD cycle:

### RED: Write Failing Test (Baseline)

Run pressure scenario with subagent WITHOUT the skill. Document exact behavior:

- What choices did they make?

- What rationalizations did they use (verbatim)?

- Which pressures triggered violations?

This is "watch the test fail" - you must see what agents naturally do before writing the skill.

### GREEN: Write Minimal Skill

Write skill that addresses those specific rationalizations. Don't add extra content for hypothetical cases.

Run same scenarios WITH skill. Agent should now comply.

### REFACTOR: Close Loopholes

Agent found new rationalization? Add explicit counter. Re-test until bulletproof.

**Testing methodology:** See @testing-skills-with-subagents.md for the complete testing methodology:

- How to write pressure scenarios

- Pressure types (time, sunk cost, authority, exhaustion)

- Plugging holes systematically

- Meta-testing techniques

## Anti-Patterns

### ❌ Narrative Example

"In session 2025-10-03, we found empty projectDir caused..."
**Why bad:** Too specific, not reusable

### ❌ Multi-Language Dilution

example-js.js, example-py.py, example-go.go
**Why bad:** Mediocre quality, maintenance burden

### ❌ Code in Flowcharts

step1 [label="import fs"];

step2 [label="read file"];