Creating GitHub Copilot Agent Skills

This skill teaches you how to create effective GitHub Copilot Agent Skills for this repository.

Pre-Check: Avoid Duplication

STOP and check before creating a new skill:

1. Does it exist already?

   • List all skills: ls -la .github/skills/
   • Read existing skill frontmatter and content
   • If semantically similar skill exists, STOP

2. Should an existing skill be expanded?

   • If frontmatter semantically matches your use case → Update existing skill's description
   • Add keywords to improve discoverability rather than creating duplicate

3. Should existing skill content change?

   • If frontmatter matches but content incomplete → Add section to existing skill
   • Enhance with additional examples, procedures, or troubleshooting
   • Update frontmatter only if significantly broadening scope

Only create new skill if:

• No semantic overlap with existing skills
• Addresses distinct problem domain
• Has unique triggering conditions

Skill Structure

Directory Placement

Skills should be placed in .github/skills/ directory:

• Project skills (repository-specific): .github/skills/skill-name/

Each skill must have its own subdirectory with a lowercase, hyphenated name that matches the name field in the frontmatter.

File Requirements

Every skill directory must contain a SKILL.md file (case-sensitive) with:

1. YAML Frontmatter (required):

2. Markdown Body with clear instructions, examples, procedures, guidelines, and references

Additional Resources

Skills can include:

• Scripts (e.g., .sh, .fsx, .ps1)
• Example files
• Templates
• Reference documentation

YAML Frontmatter Best Practices

The frontmatter is critical for skill discoverability and token efficiency:

Required Fields

• name (string): Unique identifier, lowercase with hyphens

  • Must match the directory name
  • Should be descriptive but concise
  • Example: hypothesis-driven-debugging, github-actions-failure-debugging

• description (string): When and why to use this skill

  • Should be 1-2 sentences
  • Include trigger keywords that help the AI recognize when to load the skill
  • Example: "Guide for debugging failing GitHub Actions workflows. Use this when asked to debug failing GitHub Actions workflows."
  • SEO-like optimization for LLMs: Include key terms that would appear in user requests

Optional Fields

• license (string): License for the skill (e.g., MIT, Apache-2.0)

Description Guidelines

The description is crucial for skill discoverability. Think of it like SEO for LLMs:

✅ Good descriptions (specific, actionable, keyword-rich):

• "Guide for debugging failing GitHub Actions workflows. Use this when asked to debug failing GitHub Actions workflows."
• "Systematic approach to investigating F# compiler performance issues using traces, dumps, and benchmarks."
• "Step-by-step process for analyzing test failures using hypothesis-driven debugging."

❌ Poor descriptions (vague, generic):

• "Helps with debugging"
• "Tool for testing"
• "Useful utility"

Token Efficiency

Skills should be concise to avoid wasting context tokens:

• Keep instructions focused and relevant
• Use bullet points and numbered lists
• Avoid redundant information
• Reference external resources rather than duplicating content
• The agent will only load skills when relevant, so clear descriptions help prevent unnecessary loading

Skill Content Best Practices

Structure

1. Title and Overview: Brief introduction
2. When to Use: Clear triggering conditions
3. Prerequisites: Required tools, setup, or knowledge
4. Step-by-Step Instructions: Numbered procedures
5. Examples: Concrete use cases
6. Troubleshooting: Common issues
7. References: Links to related documentation

Writing Style

• Use imperative mood ("Run the test", not "You should run the test")
• Be specific and actionable
• Include command examples with expected output
• Use code blocks with language identifiers
• Highlight warnings and critical information
• Reference tools and APIs that the agent has access to

Examples

Always include concrete examples:

• Command invocations with flags and arguments
• Expected output and how to interpret it
• Common variations and edge cases
• Links to real-world usage in the repository

Testing Your Skill

After creating a skill:

1. Verify the file structure:

   ls -la .github/skills/your-skill-name/
   # Should show SKILL.md and any additional resources

2. Validate YAML frontmatter:

   • Ensure proper YAML syntax
   • Required fields are present
   • Name matches directory name

3. Test skill invocation:

   • Ask Copilot a question that should trigger the skill
   • Verify the skill is loaded (check response for skill-specific guidance)
   • Ensure instructions are clear and actionable

4. Iterate based on usage:

   • Monitor how often the skill is used
   • Refine description for better discoverability
   • Update instructions based on feedback

Examples from This Repository

See existing skills in .github/skills/ for reference:

• hypothesis-driven-debugging: Systematic failure investigation
• Additional skills may be added over time

References

• GitHub Copilot Agent Skills Documentation
• Agent Skills Open Standard
• Community Skills Collection