writing-skills

name writing-skills description Use when creating new skills, editing existing skills, or verifying skills work before deployment Writing Skills Overview Writing skills IS Test-Driven Development applied to process documentation. Personal skills live in your runtime's skills directory ( ~/.claude/skills/ on Claude Code) — see codex-tools.md or gemini-tools.md for the path on those runtimes. Codex, Copilot CLI, and Gemini CLI all also recognize ~/.agents/skills/ as a cross-runtime alias. 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. REQUIRED BACKGROUND: You MUST understand superpowers:test-driven-development before using this skill. That skill defines the fundamental RED-GREEN-REFACTOR cycle. This skill adapts TDD to documentation. 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. What is a Skill? A skill is a reference guide for proven techniques, patterns, or tools. Skills help future agents find and apply effective approaches. 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 your instructions file) 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 SDO 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 Skill Discovery Optimization (SDO) Critical for discovery: Future agents need to FIND your skill 1. Rich Description Field Purpose: Your agent reads the 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, an agent may follow the description instead of reading the full skill content. A description saying "code review between tasks" caused an agent 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), the agent correctly read the flowchart and followed the two-stage review process. The trap: Descriptions that summarize workflow create a shortcut agents will take. The skill body becomes documentation agents skip. # ❌ BAD: Summarizes workflow - agents 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 an agent 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 5. 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 in this directory 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.