Skill Creator Agent Skill

Skill Creator for GitHub Copilot

Create and maintain skills in .github/skills/ that extend GitHub Copilot's capabilities with project-specific knowledge.

What Are Skills

Skills are SKILL.md files that provide specialized, procedural knowledge that Copilot doesn't inherently have. They turn Copilot from a general assistant into a domain expert for specific tasks in this codebase.

Skills provide:

• Specialized workflows — multi-step procedures for project-specific domains
• Domain expertise — architecture patterns, conventions, business logic
• Bundled references — detailed docs loaded only when needed

Skill Anatomy

.github/skills/
└── skill-name/
    ├── SKILL.md              (required — frontmatter + instructions)
    └── references/           (optional — detailed docs, loaded on demand)

SKILL.md Structure

---
name: my-skill-name
description: What this skill does and WHEN to use it. Include trigger words and scenarios. This is the primary mechanism for Copilot to decide whether to load the skill body.
---

# Skill Title

Concise instructions for using this skill.

## When to Use

- Bullet list of triggering scenarios

## Core Content

(workflow, patterns, examples)

Wiring the Skill

After creating the SKILL.md, register it in .github/copilot-instructions.md under the <skills> section:

<skill>
<name>my-skill-name</name>
<description>Same or similar description as in SKILL.md frontmatter</description>
<file>${workspaceFolder}\.github\skills\my-skill-name\SKILL.md</file>
</skill>

> Note: Replace ${workspaceFolder} with the absolute path to the repository root on your machine (e.g. \home\user\repos\vscode-documentdb). VS Code resolves skill file paths at runtime and currently requires absolute paths.

Copilot reads skill metadata (name + description) to decide when to trigger. The SKILL.md body is loaded only after triggering.

Core Principles

1. Concise is Key

The context window is shared with conversation history, other instructions, and user requests. Challenge each paragraph: "Does Copilot already know this?" and "Does this justify its token cost?"

• Prefer concise examples over verbose explanations
• Only include what Copilot doesn't already know — skip general TypeScript/React knowledge
• Target under 300 lines for SKILL.md body; split into references if larger

2. Progressive Disclosure

Use a three-level loading system:

• Metadata (name + description) — always visible (~50 words)
• SKILL.md body — loaded when skill triggers
• References — loaded on demand by Copilot when deeper detail is needed

For skills with multiple variants or extensive reference material, keep the core workflow in SKILL.md and move details to references/:

## Advanced Topics

- **Detailed format spec**: See [FORMAT.md](./FORMAT.md)
- **Migration patterns**: See [references/migration.md](./references/migration.md)

3. Match Freedom to Task Fragility

| Freedom Level | When | Example |

| ----------------------------------- | ------------------------- | ---------------------------- |

| High (text guidance) | Multiple valid approaches | Architecture recommendations |

| Medium (patterns with examples) | Preferred pattern exists | tRPC router creation |

| Low (exact steps) | Fragile, error-prone | Release note formatting |

4. Do NOT Include

• README.md, CHANGELOG.md, or auxiliary documentation
• Setup/installation instructions for the skill itself
• User-facing documentation — skills are for Copilot, not humans
• Information Copilot already knows (general language features, common libraries)

Skill Creation Workflow

Step 1: Understand the Domain

Identify concrete scenarios the skill addresses:

• What tasks trigger it?
• What does Copilot get wrong without it?
• What project-specific knowledge is needed?

Step 2: Plan Contents

For each scenario, determine:

• What code patterns or templates are repeatedly needed?
• What reference material should be available?
• What pitfalls must be called out?

Step 3: Write the Skill

• Create .github/skills/{skill-name}/SKILL.md
• Write frontmatter: name and description (description is the trigger — be comprehensive about when to use)
• Write body: Core workflow, patterns, examples. Keep it lean.
• Add references (optional): Split out detailed format specs, schemas, or variant-specific docs
• Register in .github/copilot-instructions.md

Step 4: Validate

• Ensure the description covers all trigger scenarios
• Verify code examples follow project conventions (see .github/copilot-instructions.md and .github/instructions/)
• Check that referenced files exist and paths are correct
• Confirm the skill doesn't duplicate information already in .github/instructions/ files

Existing Skills Reference

| Skill | Purpose |

| --------------------------- | ------------------------------------------------------ |

| writing-release-notes | Release notes and changelog generation |

| accessibility-aria-expert | Accessibility issues in React/Fluent UI webviews |

| webview-trpc-messaging | tRPC communication between extension host and webviews |

Example: Minimal Skill

---
name: my-pattern
description: Implements the XYZ pattern for this codebase. Use when creating new XYZ instances, modifying existing XYZ behavior, or debugging XYZ-related issues.
---

# XYZ Pattern

## When to Use

- Creating a new XYZ
- Modifying XYZ behavior
- Debugging XYZ issues

## Pattern

\`\`\`typescript
// core pattern example
\`\`\`

## Common Pitfalls

- Don't do X because Y
- Always do Z when W