jburlison/agent-file-specs

AI Coding Assistant Customization File Specifications

This skill provides the authoritative, up-to-date specifications for all AI coding assistant customization file types. Each file type has its own dedicated reference document with complete attribute tables, validation rules, examples, and best practices.

Standard: These specs align with the Agent Skills open standard and the VS Code Copilot customization documentation.

How to Use This Skill

1. Read the Quick Reference below to identify the file type you need.
2. Follow the link to the dedicated reference document for full details.
3. Use the File Locations reference when you need to know where files go for a specific provider.
4. Use the Settings reference for VS Code configuration.

Important: Detailed specifications live in the references/ folder — not in this file. This keeps the main skill file lightweight for efficient context loading per the progressive disclosure model.

Quick Reference

| Type | Extension | Purpose | Reference | |------|-----------|---------|-----------| | Agent | .agent.md / .md | Custom AI personas with specialized behaviors, tool restrictions, and handoff workflows | AGENTS.md | | Skill | SKILL.md (directory-based) | Reusable, portable capabilities with scripts and resources — follows the Agent Skills open standard | SKILLS.md | | Prompt | .prompt.md | Reusable prompt templates invoked as slash commands | PROMPTS.md | | Instruction | .instructions.md | Contextual guidance applied automatically by file type or description | INSTRUCTIONS.md | | File Locations | — | Provider folder mapping, directory structure, naming conventions | FILE-LOCATIONS.md | | VS Code Settings | — | Settings that control customization file discovery and behavior | SETTINGS.md |

Provider Support

These specifications work across multiple AI coding assistant providers. Each provider uses its own base folder but the file formats are consistent:

| Provider | Base Folder | |----------|-------------| | GitHub Copilot | .github/ | | Claude Code | .claude/ | | Codex | .codex/ | | OpenCode | .config/opencode/ |

See FILE-LOCATIONS.md for the complete directory structure and provider-specific details.

File Type Selection Guide

Use this decision tree to choose the right file type:

• "I want coding standards applied everywhere" → Use always-on instructions (.github/copilot-instructions.md or AGENTS.md). See INSTRUCTIONS.md.

• "I want different rules for different file types" → Use file-based instructions (.instructions.md with applyTo patterns). See INSTRUCTIONS.md.

• "I have a reusable task I run repeatedly" → Use a prompt file (.prompt.md) invoked as a slash command. See PROMPTS.md.

• "I need a multi-step workflow with scripts and resources" → Use an Agent Skill (directory with SKILL.md). Portable across tools. See SKILLS.md.

• "I need a specialized AI persona with tool restrictions" → Use a custom agent (.agent.md). Supports handoffs for multi-step workflows. See AGENTS.md.

Authoritative Sources

• VS Code Copilot Customization Overview
• VS Code Custom Agents
• VS Code Agent Skills
• VS Code Prompt Files
• VS Code Custom Instructions
• Agent Skills Specification (agentskills.io)
• Awesome Copilot (community examples)
• Anthropic Reference Skills