GitHub Copilot vs Fusion | agentconfig.ing

GitHub Copilot vs FusionComparisonUpdated 2026-03-16

SUMMARY

GitHub Copilot (IDE) uses markdown configuration while Fusion (IDE) uses mdc. They differ on 4 of 11 compared features. Both tools provide AI-assisted development but take different approaches to project configuration.

FEATURE COMPARISON

Feature	GitHub Copilot	Fusion	Notes
Config format	markdown	mdc
Hierarchy support	✓	✗	Whether config files can be placed at multiple directory levels
Global config	✗	✗	User-wide configuration outside any project
Project config	✓	✓
Subdirectory scoping	✓	✗	Config files in subdirectories that apply only to that subtree
File inclusion / imports	✗	✗	Ability to include or reference other files from config
Ignore file	✗	✗
IDE integration	✓	✓
Schema / structure	Free-form (Markdown)	Hybrid (MDC frontmatter + Markdown)	Whether config uses structured schema or free-form content
Git committed	✓	✓	Whether primary config files are intended to be version-controlled
Encoding	UTF-8	UTF-8

FILE MAPPING

Purpose	GitHub Copilot	Fusion
Project instructions	.github/copilot-instructions.md	AGENTS.md

SIDE-BY-SIDE CODE SAMPLES

GitHub Copilot

.github/copilot-instructions.md

markdown

# Copilot Instructions

## Code Style
- Use TypeScript strict mode for all new files
- Prefer functional components with hooks over class components
- Use named exports, not default exports

## Libraries
- Use date-fns for date manipulation (not moment.js)
- Use zod for runtime validation
- Prefer fetch over axios for HTTP requests

## Testing
- Write tests using Vitest
- Use Testing Library for component tests
- Aim for integration tests over unit tests

## Conventions
- Use camelCase for variables, PascalCase for components
- Prefix interfaces with I (e.g., IUserProps)
- Keep files under 300 lines; extract if longer

Fusion

.builder/rules/*.mdc

mdc

---
description: React component conventions
globs: src/components/**/*.tsx
alwaysApply: false
---

# React Component Rules

## Structure
- Use functional components with TypeScript
- Define props interface above the component
- Export components as named exports

## Styling
- Use the project design system tokens for spacing and colors
- Prefer utility classes over custom CSS
- Keep component-specific styles colocated

## Patterns
- Wrap async data in Suspense boundaries
- Use forwardRef for reusable interactive components
- Keep components under 150 lines; extract hooks for logic

## Accessibility
- All interactive elements need aria-labels
- Use semantic HTML elements (nav, main, section)
- Ensure keyboard navigation works for custom widgets

KEY DIFFERENCES

1. Config format

GitHub Copilot: markdown. Fusion: mdc.

2. Hierarchy support

GitHub Copilot: Supported. Fusion: Not supported.

3. Subdirectory scoping

GitHub Copilot: Supported. Fusion: Not supported.

4. Schema / structure

GitHub Copilot: Free-form (Markdown). Fusion: Hybrid (MDC frontmatter + Markdown).

WHICH SHOULD I USE?

Recommendation

Choose based on your IDE/CLI preference. If you use GitHub Copilot, configure .github/copilot-instructions.md. If you use Fusion, configure .builder/rules/*.mdc. Many projects include config files for multiple tools so each team member can use their preferred editor.

PORTABILITY TIP

sync-instructions.sh

bash

# Maintain a single source of truth:
cp AI-INSTRUCTIONS.md CLAUDE.md
cp AI-INSTRUCTIONS.md .cursorrules
cp AI-INSTRUCTIONS.md AGENTS.md