Fusion vs OpenCodeUpdated 2026-03-16

SUMMARY

Fusion (IDE) uses mdc configuration while OpenCode (CLI) uses markdown. They differ on 6 of 11 compared features. Both tools provide AI-assisted development but take different approaches to project configuration.

FEATURE COMPARISON

FeatureFusionOpenCode
Config formatmdcmarkdown
Hierarchy support
Global config
Project config
Subdirectory scoping
File inclusion / imports
Ignore file
IDE integrationCLI
Schema / structureHybrid (MDC frontmatter + Markdown)Free-form (Markdown)
Git committed
EncodingUTF-8UTF-8

FILE MAPPING

PurposeFusionOpenCode
Project instructionsAGENTS.mdAGENTS.md

SIDE-BY-SIDE CODE SAMPLES

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

OpenCode
AGENTS.md
markdown
# Project Instructions

## Overview
This is a TypeScript monorepo using pnpm workspaces.

## Code Style
- Use strict TypeScript with no implicit any
- Prefer functional components with hooks
- All exports should be named (no default exports)

## Architecture
- /packages/core — shared business logic
- /packages/ui — React component library
- /apps/web — Next.js frontend

## Build & Test
Run tests with: pnpm test
Build all packages: pnpm build
All PRs must have >80% coverage on changed files.

## Conventions
- Use conventional commits (feat:, fix:, chore:)
- Prefer composition over inheritance
- See @docs/api-guidelines.md for API design patterns

KEY DIFFERENCES

1. Config format

Fusion: mdc. OpenCode: markdown.

2. Hierarchy support

Fusion: Not supported. OpenCode: Supported.

3. Global config

Fusion: Not supported. OpenCode: Supported.

4. Subdirectory scoping

Fusion: Not supported. OpenCode: Supported.

5. IDE integration

Fusion: Supported. OpenCode: CLI.

6. Schema / structure

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

WHICH SHOULD I USE?

Recommendation

Choose based on your IDE/CLI preference. If you use Fusion, configure .builder/rules/*.mdc. If you use OpenCode, configure AGENTS.md. 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

SEE ALSO

agentconfig.ing2026-03-16COMPARE(1)