Skill Creator

Core Principles

Concise is key. The context window is shared with system prompts, conversation history, other skills, and the user's request. Only add context Claude doesn't already have. Challenge each piece: "Does this paragraph justify its token cost?" Prefer concise examples over verbose explanations.

Match freedom to fragility. Narrow bridge with cliffs = specific guardrails (exact scripts). Open field = many valid routes (text instructions). See references/patterns.md for detailed guidance.

Skill Structure

Folder Rules

skill-name/ # kebab-case, must match name field ├── SKILL.md # Required (exact case-sensitive spelling) ├── scripts/ # Optional: executable code ├── references/ # Optional: documentation loaded as needed └── assets/ # Optional: templates, images, fonts for output

• Folder name must be kebab-case and match the name field exactly

• No README.md or other auxiliary files (CHANGELOG, INSTALLATION_GUIDE, etc.)

• Only include files that directly support the skill's functionality

For details on when to use scripts/, references/, and assets/, see references/patterns.md .

SKILL.md Format

Frontmatter

The YAML frontmatter controls whether Claude loads the skill. This is the most important part.

name: your-skill-name description: What it does. Use when [specific trigger phrases].

Rules:

Rule Detail

name

kebab-case, no spaces/capitals, must match folder name

description

Must include WHAT it does AND WHEN to use it

Description length Under 1024 characters

Trigger phrases Include specific phrases users would say

File types Mention relevant file types if applicable (e.g., ".csv files", ".docx")

No XML tags No < or > in frontmatter (security restriction)

No reserved names No "claude" or "anthropic" in the name field

Good descriptions:

Specific, includes triggers and file types

description: Analyzes Figma design files and generates developer handoff documentation. Use when user uploads .fig files, asks for "design specs", "component documentation", or "design-to-code handoff".

Includes trigger phrases and capabilities

description: Manages Linear project workflows including sprint planning, task creation, and status tracking. Use when user mentions "sprint", "Linear tasks", "project planning", or asks to "create tickets".

Bad descriptions:

Too vague - won't trigger correctly

description: Helps with projects.

Missing triggers - Claude won't know when to load it

description: Creates sophisticated multi-page documentation systems.

Too technical, no user-facing triggers

description: Implements the Project entity model with hierarchical relationships.

Put ALL "when to use" information in the description, not in the body. The body only loads after triggering, so "When to Use This Skill" sections in the body do not help Claude decide to load the skill.

Optional fields: license (e.g., MIT), compatibility (environment requirements, 1-500 chars), metadata (author, version, mcp-server).

Body Structure

After the frontmatter, write instructions in Markdown. The recommended structure:

Skill Name

Instructions

Step 1: [First Major Step]

Clear, specific explanation with examples.

Step 2: [Next Step]

(continue as needed)

Examples

Example 1: [common scenario]

User says: "..." Actions: 1. ... 2. ... Result: ...

Troubleshooting

Error: [Common error]

Cause: [Why it happens] Solution: [How to fix]

All three sections are expected: Instructions, Examples, and Troubleshooting. Skills missing Examples or Troubleshooting are incomplete.

Writing guidelines:

• Use imperative form ("Run the script", not "You should run the script")

• Be specific and actionable — Run python scripts/validate.py --input {file} not "Validate the data"

• Include what success looks like after each step

• Reference bundled resources clearly: "Consult references/api-patterns.md for rate limiting guidance"

Size limit: Keep SKILL.md under ~5,000 words. If approaching this limit, move reference material to references/ and link to it. See references/patterns.md for progressive disclosure patterns.

Creation Process

Step 1: Understand with Concrete Examples

Understand how the skill will be used before writing anything. Ask the user:

• "What functionality should this skill support?"

• "Can you give examples of how it would be used?"

• "What would a user say that should trigger this skill?"

• "What should NOT trigger this skill?"

Avoid asking too many questions at once. Start with the most important and follow up as needed. Conclude when there is a clear sense of the functionality and trigger scenarios.

Step 2: Plan Reusable Contents

Analyze each use case example to identify what reusable resources would help:

• Scripts — Code that gets rewritten repeatedly (e.g., scripts/rotate_pdf.py for a PDF skill)

• References — Knowledge Claude needs while working (e.g., references/schema.md for a database skill)

• Assets — Files used in output (e.g., assets/template/ for a webapp builder)

Create a list of resources to include. Not every skill needs bundled resources — many skills are instructions-only.

Step 3: Initialize Directory

Create the skill directory with required SKILL.md and any needed resource directories:

mkdir -p skill-name/{scripts,references,assets} # include only dirs you need touch skill-name/SKILL.md

Step 4: Write the Skill

4a: Implement reusable resources first

Write scripts, references, and assets before SKILL.md. This may require user input (e.g., brand assets, API docs, database schemas). Test all scripts by running them.

4b: Write frontmatter

Follow the frontmatter rules above. Verify:

• Name matches folder name

• Description includes WHAT + WHEN + trigger phrases

• Description under 1024 characters

• No XML tags or reserved words

4c: Write body

Follow the recommended body structure:

• Instructions — Step-by-step workflow. Be specific and actionable. Include concrete commands, expected outputs, and decision points. Reference bundled resources where relevant.

• Examples — At least one worked example showing a user request, the actions taken, and the result. More examples for complex skills.

• Troubleshooting — Cover 2-3 common failure modes with cause and solution.

Step 5: Test and Iterate

Triggering tests

Test that the skill loads at the right times:

Should trigger:

• "Help me [primary use case]"
• "[Paraphrased request]"
• "[Domain-specific terminology]"

Should NOT trigger:

• "[Unrelated query]"
• "[Similar but different domain]"

Ask Claude: "When would you use the [skill name] skill?" — Claude will quote the description back, revealing gaps.

Functional tests

Run the skill on real tasks. Verify:

• Outputs are correct and complete

• All workflow steps execute

• Bundled resources are referenced appropriately

Iteration signals

Signal Symptom Fix

Undertriggering Skill doesn't load when it should Add more trigger phrases and keywords to description

Overtriggering Skill loads for unrelated queries Add specificity or negative triggers ("Do NOT use for...")

Execution issues Inconsistent results or user corrections needed Improve instructions, add error handling, be more specific

Context bloat Slow responses, degraded quality Move content to references/, reduce SKILL.md size

Quality Checklist

Before finalizing, verify:

• Folder is kebab-case, matches name field

• SKILL.md exists (exact case)

• Frontmatter has --- delimiters

• name : kebab-case, no spaces/capitals

• description : includes WHAT and WHEN with trigger phrases

• description : under 1024 characters

• No XML tags (<

) in frontmatter

• No "claude" or "anthropic" in name

• No README.md or auxiliary files in folder

• Instructions are specific and actionable

• Examples section included

• Troubleshooting section included

• SKILL.md under ~5,000 words

• References clearly linked from SKILL.md (if using references/)

• File types mentioned in description (if applicable)

Examples

Example: Creating a csv-analyzer skill

Step 1 — Understand: User wants a skill that analyzes CSV files, generates summary statistics, and creates visualizations. Triggers: "analyze this CSV", "summarize this data", "chart this spreadsheet".

Step 2 — Plan resources:

• scripts/analyze.py — Reusable analysis script with pandas

• No references or assets needed

Step 3 — Initialize:

csv-analyzer/ ├── SKILL.md └── scripts/ └── analyze.py

Step 4 — Write:

Frontmatter:

name: csv-analyzer description: Analyze CSV files with summary statistics and visualizations. Use when user uploads .csv files, asks to "analyze data", "summarize this CSV", "chart this spreadsheet", or wants statistical insights from tabular data.

Body includes: step-by-step workflow (load CSV, validate, analyze, visualize, present), an example showing a user asking "Summarize sales.csv" with the expected output, and troubleshooting for common issues (malformed CSV, missing columns, large files).

Step 5 — Test: Verify it triggers on "analyze this CSV" and "give me stats on this data file" but not on "help me write a CSV parser" (that's a coding task, not an analysis task).

Troubleshooting

Skill doesn't trigger

Cause: Description is too vague or missing trigger phrases. Solution: Add specific phrases users would say. Include file types if relevant. Test with: "When would you use the [skill name] skill?"

Skill triggers too often

Cause: Description is too broad. Solution: Be more specific. Add negative triggers:

description: Processes PDF legal documents for contract review. Do NOT use for general PDF editing or non-legal documents.

Instructions not followed

Cause: Instructions are too verbose, ambiguous, or buried. Solutions:

• Keep instructions concise — use bullet points and numbered lists

• Put critical instructions at the top

• Move detailed reference material to references/

• Replace ambiguous language with specific commands

• For critical validations, consider bundling a script (code is deterministic; language interpretation isn't)

Skill feels slow or quality degrades

Cause: SKILL.md is too large or too many skills enabled simultaneously. Solution: Move detailed docs to references/ , keep SKILL.md under ~5,000 words. Link to references instead of inlining content.

For advanced patterns (progressive disclosure, resource organization, domain-specific splitting), see references/patterns.md .