Writing skills IS Test-Driven Development applied to process documentation.
Personal skills live in your runtime's skills directory
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.
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 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.
Create when:
Don't create for:
Concrete method with steps to follow (condition-based-waiting, root-cause-tracing)
Way of thinking about problems (flatten-with-flags, test-invariants)
API docs, syntax guides, tool documentation (office docs)
skills/
skill-name/
SKILL.md # Main reference (required)
supporting-file.* # Only if needed
Flat namespace - all skills in one searchable namespace
Separate files for:
Keep inline:
Frontmatter (YAML):
name and description (see agentskills.io/specification for all supported fields)name: Use letters, numbers, and hyphens only (no parentheses, special chars)description: Third-person, describes ONLY when to use (NOT what it does)
---
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
Critical for discovery: Future agents need to FIND your skill
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:
# ❌ 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
Use words an agent would search for:
Use active voice, verb-first:
creating-skills not skill-creationcondition-based-waiting not async-test-helpersProblem: getting-started and frequently-referenced skills load into EVERY conversation. Every token counts.
Target word counts:
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:
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-helpersusing-skills not skill-usageflatten-with-flags > data-structure-refactoringroot-cause-tracing > debugging-techniquesGerunds (-ing) work well for processes:
creating-skills, testing-skills, debugging-with-logsWhen writing documentation that references other skills:
Use skill name only, with explicit requirement markers:
**REQUIRED SUB-SKILL:** Use superpowers:test-driven-development**REQUIRED BACKGROUND:** You MUST understand superpowers:systematic-debuggingSee skills/testing/test-driven-development (unclear if required)@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.
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:
Never use flowcharts for:
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
One excellent example beats many mediocre ones
Choose most relevant language:
Good example:
Don't:
You're good at porting - one great example is enough.
defense-in-depth/
SKILL.md # Everything inline
When: All content fits, no heavy reference needed
condition-based-waiting/
SKILL.md # Overview + patterns
example.ts # Working helpers to adapt
When: Tool is reusable code, not just narrative
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
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:
REQUIRED BACKGROUND: The superpowers:test-driven-development skill explains why this matters. Same principles apply to documentation.
Different skill types need different test approaches:
Examples: TDD, verification-before-completion, designing-before-coding
Test with:
Success criteria: Agent follows rule under maximum pressure
Examples: condition-based-waiting, root-cause-tracing, defensive-programming
Test with:
Success criteria: Agent successfully applies technique to new scenario
Examples: reducing-complexity, information-hiding concepts
Test with:
Success criteria: Agent correctly identifies when/how to apply pattern
Examples: API documentation, command references, library guides
Test with:
Success criteria: Agent finds and correctly applies reference information
| 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.
Before writing guidance, classify the baseline failure. The form that bulletproofs one failure type measurably backfires on another.
| Baseline failure | Right form | Wrong form |
|---|---|---|
| Skips/violates a rule under pressure (knows better, does it anyway) | Prohibition + rationalization table + red flags (see Bulletproofing below) | Soft guidance ("prefer...", "consider...") |
| Complies, but output has the wrong shape (bloated prompt, buried verdict, restated spec) | Positive recipe or contract: state what the output IS — its parts, in order | Prohibition list ("don't restate", "never narrate") |
| Omits a required element from something they already produce | Structural: REQUIRED field or slot in the template they fill in | Prose reminders near the template |
| Behavior should depend on a condition | Conditional keyed to an observable predicate ("if the brief exists, reference it") | Unconditional rule + exemption clauses |
Why prohibitions backfire on shaping problems: under a competing incentive ("make the prompt self-contained"), agents negotiate with "don't X". In head-to-head wording tests on dispatch-prompt guidance, the prohibition arm produced clearly more of the unwanted content than the recipe arm (fully separated distributions), and trended worse than even the no-guidance control — micro-test your own case rather than assuming, but never reach for the prohibition by default. A recipe leaves nothing to negotiate: the output matches the stated shape or it doesn't.
Rules for whichever form you pick:
Skills that enforce discipline (like TDD) need to resist rationalization. Agents are smart and will find loopholes when under pressure.
Scope: this toolkit is for discipline failures — an agent that knows the rule and skips it under pressure. For wrong-shaped output or omitted elements, prohibition-based bulletproofing backfires; use the forms in Match the Form to the Failure instead.
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.
Don't just state the rule - forbid specific workarounds:
<Bad> ```markdown Write code before test? Delete it. ``` </Bad> <Good> ```markdown Write code before test? Delete it. Start over.No exceptions:
</Good>
### Address "Spirit vs Letter" Arguments
Add foundational principle early:
```markdown
**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.
Capture rationalizations from baseline testing (see Testing section below). Every excuse agents make goes in the table:
| Excuse | Reality |
|--------|---------|
| "Too simple to test" | Simple code breaks. Test takes 30 seconds. |
| "I'll test after" | Tests passing immediately prove nothing. |
| "Tests after achieve same goals" | Tests-after = "what does this do?" Tests-first = "what should this do?" |
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.**
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
Follow the TDD cycle:
Run pressure scenario with subagent WITHOUT the skill. Document exact behavior:
This is "watch the test fail" - you must see what agents naturally do before writing the 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.
Agent found new rationalization? Add explicit counter. Re-test until bulletproof.
Full pressure-scenario runs are the final gate, but they are slow and expensive per iteration. Verify the wording itself first with micro-tests:
Micro-tests verify wording; they do not replace pressure scenarios for discipline skills.
Testing methodology: See testing-skills-with-subagents.md for the complete testing methodology:
"In session 2025-10-03, we found empty projectDir caused..." Why bad: Too specific, not reusable
example-js.js, example-py.py, example-go.go Why bad: Mediocre quality, maintenance burden
step1 [label="import fs"];
step2 [label="read file"];
Why bad: Can't copy-paste, hard to read
helper1, helper2, step3, pattern4 Why bad: Labels should have semantic meaning
After writing ANY skill, you MUST STOP and complete the deployment process.
Do NOT:
The deployment checklist below is MANDATORY for EACH skill.
Deploying untested skills = deploying untested code. It's a violation of quality standards.
IMPORTANT: Create a todo for EACH checklist item below.
RED Phase - Write Failing Test:
GREEN Phase - Write Minimal Skill:
name and description fields (max 1024 chars; see spec)REFACTOR Phase - Close Loopholes:
Quality Checks:
Deployment:
How future agents find your skill:
Optimize for this flow - put searchable terms early and often.
Creating skills IS TDD for process documentation.
Same Iron Law: No skill without failing test first. Same cycle: RED (baseline) → GREEN (write skill) → REFACTOR (close loopholes). Same benefits: Better quality, fewer surprises, bulletproof results.
If you follow TDD for code, follow it for skills. It's the same discipline applied to documentation.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
CLI to manage emails via IMAP/SMTP. Use `himalaya` to list, read, write, reply, forward, search, and organize emails from the terminal. Supports multiple accounts and message composition with MML (MIME Meta Language).
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
CLI to manage emails via IMAP/SMTP. Use `himalaya` to list, read, write, reply, forward, search, and organize emails from the terminal. Supports multiple accounts and message composition with MML (MIME Meta Language).