agentconfig.ing
Fusion vs WindsurfUpdated 2026-03-16

SUMMARY

Fusion (IDE) uses mdc configuration while Windsurf (IDE) 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

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

FILE MAPPING

PurposeFusionWindsurf
Project rules.builder/rules/*.mdc.windsurf/rules/*.md
Project rules.builderrulesAGENTS.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
Windsurf
.windsurf/rules/*.md
markdown
---
trigger: glob
globs: "**/*.test.ts"
---

# Testing Conventions

- Use Vitest as the test runner
- Colocate test files next to source files
- Use describe blocks organized by function/component name
- Prefer userEvent over fireEvent in component tests
- Mock external services; never hit real APIs in unit tests

KEY DIFFERENCES

1. Config format

Fusion: mdc. Windsurf: markdown.

2. Hierarchy support

Fusion: Not supported. Windsurf: Supported.

3. Global config

Fusion: Not supported. Windsurf: Supported.

4. Subdirectory scoping

Fusion: Not supported. Windsurf: Supported.

5. Ignore file

Fusion: Not supported. Windsurf: .codeiumignore.

6. Schema / structure

Fusion: Hybrid (MDC frontmatter + Markdown). Windsurf: 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 Windsurf, configure .windsurfrules. 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)