Copilot Agent Chat Implementation

Use this skill when setting up repository structures and file schemas for .github/copilot-instructions.md, .github/instructions/*.instructions.md, .github/prompts/*.prompt.md, .github/agents/*.agent.md, and .github/skills/<skill>/SKILL.md.

File Type Reference

1. Always-On Instructions — .github/copilot-instructions.md

• •Automatically applied to every chat request in the workspace
• •No frontmatter required — plain Markdown
• •Use for: coding standards, architecture decisions, library preferences, security requirements

2. Scoped Instructions — .github/instructions/*.instructions.md

Required frontmatter:

---
description: "Short description shown on hover"
applyTo: '**/*.py'   # Glob pattern — omit to use semantic matching only
---

Applied when: a file matching applyTo is active, or when the description semantically matches the task.

3. Reusable Prompts — .github/prompts/*.prompt.md

Required frontmatter:

---
description: "What this prompt does"
agent: 'agent'        # Use 'agent' for full agentic mode
tools: ['search', 'edit', 'read', 'problems', 'execute']
argument-hint: "${input:myVariable}"   # Optional input placeholder
---

Invoked via /prompt-name slash command in Copilot Chat.

4. Custom Agents — .github/agents/*.agent.md

Required frontmatter:

---
description: "Agent specialisation description"
name: My Agent Name
tools: ['search', 'edit', 'execute', 'read', 'problems']
model: 'Claude Sonnet 4.5'
target: 'vscode'
infer: true
handoffs:
  - label: "Review Security"
    agent: security-review    # Must match another .agent.md filename (without extension)
---

Invoked via @agent-name in Copilot Chat.

5. Project Skills — .github/skills/<name>/SKILL.md

Required frontmatter:

---
name: skill-name          # Must match parent directory name exactly (lowercase, hyphens)
description: >            # Max 1024 chars; specific about when to trigger
  Detailed trigger description...
argument-hint: "[...]"    # Optional
user-invokable: true      # Optional, default true
---

Directory Structure

.github/
├── copilot-instructions.md
├── instructions/
│   └── *.instructions.md
├── prompts/
│   └── *.prompt.md
├── agents/
│   └── *.agent.md
└── skills/
    └── <skill-name>/
        └── SKILL.md

Core Requirements

• •Place always-on rules in .github/copilot-instructions.md
• •Place scoped rules in .github/instructions/*.instructions.md with description and applyTo frontmatter
• •Place reusable prompts in .github/prompts/*.prompt.md with description, agent, tools
• •Place custom agents in .github/agents/*.agent.md with description, tools, model, target
• •Place skills in .github/skills/<skill-name>/SKILL.md with name matching directory, and description

Reliability Checks

• •Use VS Code Chat Diagnostics (Ctrl+Shift+P → "GitHub Copilot: Diagnostics") to verify loaded files
• •Ensure applyTo glob patterns match active files
• •Ensure name in SKILL.md frontmatter matches the parent directory name exactly
• •Ensure agent handoffs reference existing .agent.md filenames
• •Keep descriptions explicit and keyword-rich so discovery triggers correctly

Common Failure Causes