{"slug":"writing-skills-4","title":"writing-skills","summary":"Use when creating new skills, editing existing skills, or verifying skills work before deployment","platform":"Claude","tags":[],"authorName":"LLM Mart","authorSlug":"llm-mart","score":0,"source":"github","price":null,"verified":false,"createdAt":"2026-09-15T18:23:37.387742Z","repo":{"url":"https://github.com/GanyuanRan/Aegis","stars":1224,"forks":53,"license":"MIT","updatedAt":"2026-09-20T11:25:37Z"},"bodyHtml":"
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name: writing-skills\ndescription: \"Use when creating new skills, editing existing skills, or verifying skills work before deployment\"

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Writing Skills

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Overview

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Writing skills uses pressure-scenario validation, not a code TDD route.

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Personal skills live in agent-specific directories (~/.claude/skills for Claude Code, ~/.agents/skills/ for Codex)

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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).

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

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Validation requirement: Skill changes need a baseline pressure scenario and\npost-change validation even when TDD mode is off; this does not require\nloading aegis:test-driven-development.

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Official guidance: For Anthropic's official skill authoring best practices, see anthropic-best-practices.md. This document provides additional patterns and guidelines that complement the TDD-focused approach in this skill.

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Bare filenames in this skill refer to files relative to this skill directory\nunless stated otherwise.

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What is a Skill?

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

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

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

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Validation Mapping for Skills

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Validation stepSkill Creation
Test casePressure scenario with subagent
Production codeSkill document (SKILL.md)
Test fails (RED)Agent violates rule without skill (baseline)
Test passes (GREEN)Agent complies with skill present
RefactorClose loopholes while maintaining compliance
Write test firstRun baseline scenario BEFORE writing skill
Watch it failDocument exact rationalizations agent uses
Minimal codeWrite skill addressing those specific violations
Watch it passVerify agent now complies
Refactor cycleFind new rationalizations → plug → re-verify
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The entire skill creation process follows RED-GREEN-REFACTOR.

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When to Create a Skill

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Create when:

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Don't create for:

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Skill Types

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Technique

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

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Pattern

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

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Reference

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

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Directory Structure

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Repository canonical source layout:

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skills/\n  skill-name/\n    SKILL.md              # Main reference (required)\n    supporting-file.*     # Only if needed\n
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Flat namespace - all skills in one searchable namespace

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Hosts may expose installed or generated views of the same skill content through\ndifferent discovery roots while preserving this repository layout as the\ncanonical source tree.

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Separate files for:

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  1. Heavy reference (100+ lines) - API docs, comprehensive syntax
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  2. Reusable tools - Scripts, utilities, templates
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Keep inline:

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SKILL.md Structure

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Frontmatter (YAML):

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---\nname: Skill-Name-With-Hyphens\ndescription: Use when [specific triggering conditions and symptoms]\n---\n\n# Skill Name\n\n## Overview\nWhat is this? Core principle in 1-2 sentences.\n\n## When to Use\n[Small inline flowchart IF decision non-obvious]\n\nBullet list with SYMPTOMS and use cases\nWhen NOT to use\n\n## Core Pattern (for techniques/patterns)\nBefore/after code comparison\n\n## Quick Reference\nTable or bullets for scanning common operations\n\n## Implementation\nInline code for simple patterns\nLink to file for heavy reference or reusable tools\n\n## Common Mistakes\nWhat goes wrong + fixes\n\n## Real-World Impact (optional)\nConcrete results\n
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Claude Search Optimization (CSO)

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Critical for discovery: Future Claude needs to FIND your skill

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1. Rich Description Field

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

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

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CRITICAL: Description = Trigger Conditions, NOT Workflow Summary

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The description should describe triggering conditions. It may mention the\nuser-facing capability or outcome when that helps answer \"Should I read this\nskill right now?\" Do NOT summarize the skill's process or workflow in the\ndescription.

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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).

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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.

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

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# ❌ BAD: Summarizes workflow - Claude may follow this instead of reading skill\ndescription: Use when executing plans - dispatches subagent per task with code review between tasks\n\n# ❌ BAD: Too much process detail\ndescription: Use for TDD - write test first, watch it fail, write minimal code, refactor\n\n# ✅ GOOD: Just triggering conditions, no workflow summary\ndescription: Use when executing implementation plans with independent tasks in the current session\n\n# ✅ GOOD: Triggering conditions only\ndescription: Use when the user explicitly requests strict or test-first TDD, or when the current conversation already contains an explicit `TDD Route: strict` decision from another Aegis workflow.\n
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Content:

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# ❌ BAD: Too abstract, vague, doesn't include when to use\ndescription: For async testing\n\n# ❌ BAD: First person\ndescription: I can help you with async tests when they're flaky\n\n# ❌ BAD: Mentions technology but skill isn't specific to it\ndescription: Use when tests use setTimeout/sleep and are flaky\n\n# ✅ GOOD: Starts with \"Use when\", describes problem, no workflow\ndescription: Use when tests have race conditions, timing dependencies, or pass/fail inconsistently\n\n# ✅ GOOD: Technology-specific skill with explicit trigger\ndescription: Use when using React Router and handling authentication redirects\n
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2. Keyword Coverage

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Use words Claude would search for:

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3. Descriptive Naming

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Use active voice, verb-first:

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4. Token Efficiency (Critical)

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

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Target word counts:

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Techniques:

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Move details to tool help:

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# ❌ BAD: Document all flags in SKILL.md\nsearch-conversations supports --text, --both, --after DATE, --before DATE, --limit N\n\n# ✅ GOOD: Reference --help\nsearch-conversations supports multiple modes and filters. Run --help for details.\n
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Use cross-references:

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# ❌ BAD: Repeat workflow details\nWhen searching, dispatch subagent with template...\n[20 lines of repeated instructions]\n\n# ✅ GOOD: Reference other skill\nAlways use subagents (50-100x context savings). REQUIRED: Use [other-skill-name] for workflow.\n
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Compress examples:

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# ❌ BAD: Verbose example (42 words)\nyour human partner: \"How did we handle authentication errors in React Router before?\"\nYou: I'll search past conversations for React Router authentication patterns.\n[Dispatch subagent with search query: \"React Router authentication error handling 401\"]\n\n# ✅ GOOD: Minimal example (20 words)\nPartner: \"How did we handle auth errors in React Router?\"\nYou: Searching...\n[Dispatch subagent → synthesis]\n
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Eliminate redundancy:

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Verification:

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wc -w skills/path/SKILL.md\n# getting-started workflows: aim for <150 each\n# Other frequently-loaded: aim for <200 total\n
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Name by what you DO or core insight:

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Gerunds (-ing) work well for processes:

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4. Cross-Referencing Other Skills

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When writing documentation that references other skills:

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Use skill name only, with explicit requirement markers:

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

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Flowchart Usage

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digraph when_flowchart {\n    \"Need to show information?\" [shape=diamond];\n    \"Decision where I might go wrong?\" [shape=diamond];\n    \"Use markdown\" [shape=box];\n    \"Small inline flowchart\" [shape=box];\n\n    \"Need to show information?\" -> \"Decision where I might go wrong?\" [label=\"yes\"];\n    \"Decision where I might go wrong?\" -> \"Small inline flowchart\" [label=\"yes\"];\n    \"Decision where I might go wrong?\" -> \"Use markdown\" [label=\"no\"];\n}\n
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Use flowcharts ONLY for:

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Never use flowcharts for:

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

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

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./render-graphs.js ../some-skill           # Each diagram separately\n./render-graphs.js ../some-skill --combine # All diagrams in one SVG\n
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Code Examples

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One excellent example beats many mediocre ones

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Choose most relevant language:

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Good example:

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Don't:

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

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File Organization

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Self-Contained Skill

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defense-in-depth/\n  SKILL.md    # Everything inline\n
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When: All content fits, no heavy reference needed

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Skill with Reusable Tool

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condition-based-waiting/\n  SKILL.md    # Overview + patterns\n  example.ts  # Working helpers to adapt\n
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When: Tool is reusable code, not just narrative

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Skill with Heavy Reference

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pptx/\n  SKILL.md       # Overview + workflows\n  pptxgenjs.md   # 600 lines API reference\n  ooxml.md       # 500 lines XML structure\n  scripts/       # Executable tools\n
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When: Reference material too large for inline

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The Validation Rule

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NO SKILL CHANGE WITHOUT A BASELINE BEHAVIOR SCENARIO\n
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This applies to NEW skills AND EDITS to existing skills.

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Write skill before testing? Delete it. Start over.\nEdit skill without testing? Same violation.

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No exceptions:

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This rule protects skill quality independently of aegis:test-driven-development.

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Testing All Skill Types

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Different skill types need different test approaches:

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Discipline-Enforcing Skills (rules/requirements)

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

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Test with:

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Success criteria: Agent follows rule under maximum pressure

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Technique Skills (how-to guides)

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

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Test with:

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Success criteria: Agent successfully applies technique to new scenario

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Pattern Skills (mental models)

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Examples: reducing-complexity, information-hiding concepts

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Test with:

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

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Reference Skills (documentation/APIs)

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Examples: API documentation, command references, library guides

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Test with:

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Success criteria: Agent finds and correctly applies reference information

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Common Rationalizations for Skipping Testing

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ExcuseReality
\"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.
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All of these mean: Test before deploying. No exceptions.

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Bulletproofing Skills Against Rationalization

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

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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.

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Close Every Loophole Explicitly

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

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