CSS First
An advanced MCP (Model Context Protocol) server that provides intelligent, context-aware CSS-first solutions for UI implementation tasks. Features semantic analysis, framework detection, and intelligent ranking with direct MDN integration.
Setup
Choose between Remote MCP (Server-Sent Events) or Local MCP (stdio) installation:
🌐 Remote MCP via SSE (Recommended)
Connect to our hosted Cloudflare Worker instance - no local installation required:
URL: https://mcp-css-first.chylik-lukas.workers.dev/sse
Claude Desktop
Add to ~/Library/Application Support/Claude/claude_desktop_config.json:
{
"mcpServers": {
"css-first-remote": {
"url": "https://mcp-css-first.chylik-lukas.workers.dev/sse",
"transport": "sse"
}
}
}
Cursor / Windsurf / Cline
Add to your MCP settings:
{
"mcpServers": {
"css-first-remote": {
"serverUrl": "https://mcp-css-first.chylik-lukas.workers.dev/mcp"
}
}
}
Claude Code CLI
Edit ~/.config/claude/config.json and add:
{
"mcpServers": {
"css-first-remote": {
"url": "https://mcp-css-first.chylik-lukas.workers.dev/sse",
"transport": "sse"
}
}
}
💻 Local MCP via stdio
Install and run locally using npm package:
Claude Desktop
Add to ~/Library/Application Support/Claude/claude_desktop_config.json:
{
"mcpServers": {
"css-first": {
"command": "npx",
"args": ["-y", "@depthark/css-first"]
}
}
}
Cursor
Add to MCP settings (.cursor/mcp_settings.json or via Settings UI):
{
"mcpServers": {
"css-first": {
"command": "npx",
"args": ["-y", "@depthark/css-first"]
}
}
}
Windsurf
Add to MCP configuration:
{
"mcpServers": {
"css-first": {
"command": "npx",
"args": ["-y", "@depthark/css-first"]
}
}
}
Cline (VS Code Extension)
Add to Cline MCP settings:
{
"mcpServers": {
"css-first": {
"command": "npx",
"args": ["-y", "@depthark/css-first"]
}
}
}
Claude Code CLI
claude mcp add css-first npx -y @depthark/css-first
Codex
Add to mcp_servers.toml:
[mcp_servers.css-first]
command = "npx"
args = ["-y", "@depthark/css-first"]
Zed Editor
Add to Zed settings:
{
"context_servers": {
"css-first": {
"command": {
"path": "npx",
"args": ["-y", "@depthark/css-first"]
}
}
}
}
🚀 Deploy Your Own Remote Instance
Deploy your own Cloudflare Worker:
git clone https://github.com/luko248/css-first
cd css-first
bun install
bun run build:core
bun run deploy:worker
Then use your custom URL:
https://mcp-css-first.<your-subdomain>.workers.dev/sse
Usage
After adding the configuration:
- Restart your MCP client
- Ask CSS questions like:
- "Create a responsive card layout"
- "Center a div vertically and horizontally"
- "Add dark mode support"
- "Make a sticky header"
- "Create organic rounded corners with corner-shape"
- "Design modern buttons with superellipse curves"
🚀 Key Features
Intelligent Analysis
- Semantic Intent Recognition: Understands user intent through advanced pattern matching (layout, animation, spacing, etc.)
- Confidence Scoring: Provides transparency with confidence levels for suggestions
- Context-Aware Keywords: Enhanced keyword extraction with semantic understanding
Project Context Awareness
- Framework Detection: Automatically detects React, Vue, Angular, Svelte projects
- CSS Framework Recognition: Supports Tailwind, Bootstrap, Material-UI, Chakra UI
- Build Tool Integration: Recognizes Webpack, Vite, Parcel, Rollup environments
- Constraint Analysis: Understands project constraints (performance, accessibility, responsive)
Enhanced MDN Integration
- Direct MDN Parsing: Pulls property data straight from MDN pages
- Performance Caching: 1-hour intelligent caching for improved response times
- Real-time Browser Support: Compatibility data derived from MDN content
Intelligent Ranking
- Relevance Scoring: Suggestions ranked by intent match, browser support, and framework compatibility
- Category-Prioritized Search: Focuses on most relevant CSS feature categories
- Framework-Specific Recommendations: Tailored advice for your tech stack
User Experience
- Consent-Driven Workflow: User approval required before property recommendations
- Detailed Analysis: Optional semantic analysis breakdown for transparency
- Implementation Guidance: Framework-specific best practices and code examples
Development Installation
For contributors and advanced users who want to modify the source:
git clone https://github.com/luko248/css-first
cd css-first
bun install
bun run build
Development Usage
For development/testing with local builds:
{
"mcpServers": {
"@depthark/css-first": {
"command": "node",
"args": ["/absolute/path/to/css-first/packages/cli/dist/cli.js"]
}
}
}
Available Tools
1. suggest_css_solution ⭐
Enhanced CSS-first solution suggester with semantic analysis, context awareness, and intelligent ranking.
Parameters:
task_description(string): Description of the UI task or problem to solvepreferred_approach(optional): 'modern', 'compatible', or 'progressive'target_browsers(optional): Array of target browsers/versionsproject_context(optional): Project context (framework, existing CSS patterns, constraints) NEWinclude_analysis(optional): Include semantic analysis details in response NEWbaseline(optional): CSS Baseline availability filter: "Widely Available", "Newly Available", "Limited Availability", "Experimental" (fetched from MDN; falls back to support-level heuristics if unavailable)max_suggestions(optional): Limit number of suggestions (default 3)response_detail(optional): "compact" (default) or "full" response fields- compact returns minimal fields (property, description, support_level, baseline, overall_support, mdn_url)
Examples:
Basic Usage:
{
"task_description": "I need to center a div horizontally and vertically",
"preferred_approach": "modern"
}
With Project Context:
{
"task_description": "Create a responsive card layout with hover animations",
"preferred_approach": "modern",
"project_context": "React project using Tailwind CSS, targeting Chrome 90+, performance-critical",
"include_analysis": true
}
With Baseline Filter:
{
"task_description": "Create a tooltip",
"baseline": "Experimental"
}
Full Response Fields:
{
"task_description": "Create a tooltip",
"response_detail": "full",
"max_suggestions": 5
}
Response includes:
- Intelligently ranked CSS suggestions
- Framework-specific recommendations
- Semantic analysis breakdown (optional)
- Confidence scoring and intent detection
- Baseline availability labels with emoji color tags
- Support level derived from MDN browser data
- Compact responses by default to reduce token usage
2. check_css_browser_support
Checks browser support for specific CSS properties using MDN data.
Parameters:
css_property(string): CSS property name to checkinclude_experimental(optional boolean): Include experimental features
Example:
{
"css_property": "flexbox",
"include_experimental": false
}
3. get_css_property_details
Retrieves comprehensive information about a CSS property from MDN documentation.
Parameters:
css_property(string): CSS property name to get details forinclude_examples(optional boolean): Include code examples
Example:
{
"css_property": "grid",
"include_examples": true
}
4. confirm_css_property_usage
Confirms user consent for using a specific CSS property and provides implementation guidance.
Parameters:
css_property(string): CSS property name user wants to useuser_consent(boolean): User consent to use this CSS propertyfallback_needed(optional boolean): Whether fallback solutions are needed
Example:
{
"css_property": "container-queries",
"user_consent": true,
"fallback_needed": true
}
🧠 How It Works
Intelligent Analysis Pipeline
-
Semantic Intent Recognition: Advanced regex patterns analyze task descriptions to understand user intent (layout, animation, spacing, responsive, visual, interaction)
-
Project Context Analysis: Detects frameworks, CSS libraries, build tools, and constraints from project context string
-
MDN Integration:
- Direct MDN parsing for property details and support data
- Caching: 1-hour intelligent cache for performance
-
Intelligent Ranking: Scores suggestions based on:
- Intent match relevance
- Browser support level
- Framework compatibility
- User confidence multiplier
-
Context-Aware Recommendations: Provides framework-specific guidance and best practices
-
User Consent & Implementation: Consent-driven workflow with detailed implementation guidance
Example Analysis Flow
Input: "Create a responsive navigation menu with smooth animations"
↓
Intent Detection: layout + responsive + animation (85% confidence)
↓
Context: React + Tailwind detected
↓
Ranked Suggestions:
1. Flexbox layout (95% support) + CSS transitions
2. CSS Grid (92% support) + transform animations
3. Container queries (75% support) with fallbacks
↓
Framework Recommendations: "Use Tailwind's responsive prefixes", "Consider React transition components"
Development
# Install dependencies
bun install
# Build all packages
bun run build
# Build specific packages
bun run build:core # @css-first/core
bun run build:cli # @depthark/css-first
# Type check
bun run typecheck
# Lint code
bun run lint
# Deploy to Cloudflare Workers
bun run deploy:worker
# Publish CLI to npm
bun run publish:cli
📁 Project Structure (Bun Monorepo)
packages/
├── core/ # @css-first/core - shared CSS services
│ └── src/
│ ├── index.ts # CSS services entry point
│ ├── types.ts # TypeScript interfaces and enums
│ ├── mdnClient.ts # MDN client and parser
│ ├── suggestions.ts # Semantic analysis and intelligent ranking
│ ├── guidance.ts # Implementation guidance
│ ├── contextAnalyzer.ts # Project context detection
│ └── features/ # Modular CSS feature definitions
│ ├── animation/ # Animation and transition features
│ ├── layout/ # Flexbox, Grid features
│ ├── logical/ # Logical properties
│ ├── responsive/ # Responsive design
│ ├── visual/ # Visual effects
│ └── ... # More feature modules
├── cli/ # @depthark/css-first - npm package
│ └── src/
│ └── index.ts # MCP server (stdio/HTTP transport)
└── worker/ # @css-first/worker - Cloudflare Workers
├── src/
│ └── index.ts # McpAgent class for remote MCP (SSE)
└── wrangler.toml # Worker-specific config
Key Architecture Benefits
- Monorepo Structure: Shared core, separate deployments (npm + Cloudflare)
- Modular Design: Each CSS category has dedicated modules for maintainability
- Semantic Analysis: Intent recognition and confidence scoring for accuracy
- Context Awareness: Framework and project constraint detection
- Performance Optimized: Intelligent caching and ranked results
- Dual Deployment: Local CLI via npm, remote MCP via Cloudflare Workers
🎯 CSS Feature Coverage
Intelligent Categories
The enhanced system provides context-aware suggestions across:
- Layout 🏗️: Flexbox, Grid, positioning, display modes
- Animation ✨: CSS animations, transitions, transforms
- Responsive 📱: Container queries, media queries, viewport units
- Visual 🎨: Shadows, gradients, borders, effects
- Interaction 🖱️: Hover states, focus, active, disabled
- Logical Properties 📐: Writing-mode aware spacing and sizing
- HTML APIs 🧩: Dialogs, popovers, invoker commands
- Typography 📝: Font properties, text alignment, spacing
- Positioning 📍: Static, relative, absolute, fixed, sticky
Supported Feature Catalog
Logical Spacing
- Logical Spacing Properties
- Modern CSS Units
Layout (Flexbox)
- Flexbox
Layout (Grid)
- CSS Grid
- CSS Subgrid
Animation
- CSS Transitions
- CSS Animations
- CSS @starting-style
- CSS interpolate-size
- CSS Scroll Timeline
- CSS View Timeline
- CSS Animation Timeline
- CSS Animation Range
- CSS View Timeline Inset
- CSS Timeline Scope
- CSS View Transitions
Visual
- CSS Gradients
- CSS Transforms
- Logical Border Properties
- CSS Overflow
- CSS Overflow Clip
- CSS Overscroll Behavior
- CSS Corner Shape
- CSS -webkit-box-reflect
Responsive
- Media Queries
Interaction
- CSS Scroll Snap
- Modern CSS Carousel with Pseudo-Elements
Selectors
- Basic Selectors
- Attribute Selectors
- State Pseudo-classes
- Structural Pseudo-classes
- Modern Selectors
- Pseudo-elements
- Form Validation Selectors
Logical
- CSS if() Function
HTML
- Invoker Commands
- Dialog closedby Attribute
Positioning
- CSS Anchor Positioning
- Anchor Positioning with Container Queries
- Anchor Name
- Position Anchor
- Position Area
- Position Try Properties
- Position Visibility
- Position Try At-Rule
- Anchor Functions
Display
- CSS Display Property
- Display Contents
- Flexbox Display
- Grid Display
- Inline Display Values
- Block Display Values
- Table Display Values
- Display None
- List Item Display
- Flow Root Display
- Subgrid Display
Modern: Container & Queries
- CSS Container Queries
- CSS Container Style Queries
- CSS Container Scroll State Queries
- CSS Anchor Positioning
- Anchor Positioning with Container Queries
- Expanded Range Syntax
Modern: Layout & Sizing
- CSS Subgrid
- CSS Masonry Layout
- CSS Grid Lanes (Masonry)
- CSS Sizing Properties
- Flexbox gap Property
- Enhanced Logical Properties
- Mobile Viewport Heights
- Stretch Sizing Keyword
- CSS aspect-ratio
- CSS Nesting
Modern: Color & Visual
- CSS color-mix() Function
- CSS color-contrast() Function
- CSS accent-color
- CSS color-scheme
- CSS light-dark() Function
- Enhanced Light-Dark Theme System
- CSS backdrop-filter
- CSS conic-gradient
- CSS image-set() Function
- Enhanced Text Decoration
- Enhanced font-variant Properties
- Text Box Trim
Modern: Motion & Transitions
- Scroll-driven Animations
- Scroll-triggered Animations
- CSS View Transitions
- View Transition Group Property
- Scoped View Transitions
Modern: Interaction & UI Patterns
- CSS Carousel with Modern Pseudo-Elements
- Scroll-Driven Carousel Animations
- CSS-Only Form Validation
- CSS-Only Modal/Dialog
- CSS-Only Tabs/Accordion
- CSS-Only Navigation Patterns
- CSS-Only Loading/Skeleton
- Popover API
- Interest Invokers
- Scroll Target Group
Modern: Media & Environment
- Enhanced prefers-* Media Queries
- CSS forced-colors Media Query
- CSS env() Function
- CSS scroll-behavior
- CSS overscroll-behavior
Modern: Functions & Syntax
- CSS Enhanced Math Functions
- CSS if() Conditional Function
- CSS Custom Functions (@function)
- CSS shape() Function
- Advanced attr() Function
- Tree Counting Functions
- Customizable Select Element
Framework-Specific Features
- React: Component-scoped styling, CSS-in-JS patterns
- Vue: Scoped styles, transition components
- Angular: ViewEncapsulation, Material Design integration
- Svelte: Built-in scoped styling, reactive CSS
CSS Framework Integration
- Tailwind: Utility-first patterns, responsive prefixes
- Bootstrap: Grid system, utility classes
- Material-UI: Theme customization, sx props
- Chakra UI: Design system tokens
📊 Enhanced Browser Support Levels
- Excellent (95%+): ✅ Safe for production use
- Good (85%+): ⚠️ Consider fallbacks for legacy browsers
- Moderate (70%+): ⚡ Use with caution and provide fallbacks
- Limited (<70%): 🔄 Consider alternative approaches
- Experimental (varies): 🧪 Cutting-edge features with progressive enhancement
✅ CSS Baseline Availability
Baseline labels are fetched from MDN and kept current; if MDN doesn't expose a Baseline status for a property, the server falls back to the support-level heuristic.
When you pass the baseline parameter, responses include an emoji tag per suggestion:
- 🟢 Widely Available: broadly supported and safe for most production usage
- 🔵 Newly Available: recently supported, validate target browsers
- 🟡 Limited Availability: spotty support; use progressive enhancement
- 🟣 Experimental: likely behind flags or drafts; only for experiments
🔧 Automated Feature Discovery
This MCP features automated CSS feature discovery using MDN documentation. The system continuously discovers and integrates recent CSS features (2021-2025) with intelligent categorization.
Automated Feature Discovery
- 🤖 Auto-Discovery: Automatically finds and categorizes new CSS features from MDN
- 📊 Intelligent Categorization: Uses semantic analysis to categorize features by type
- 🔄 Continuous Updates: Built-in mechanisms for ongoing feature maintenance
- 📈 Browser Support Analysis: Automatic extraction of compatibility information
Recently Integrated Features (2021-2025)
🆕 Major CSS Features Added
- Container Queries (2022): Element-based responsive design with logical units (
cqi,cqb) and style/scroll queries - CSS Nesting (2023): Native CSS nesting without preprocessors
- :has() Pseudo-class (2022): Parent selection based on children
- Dynamic Viewport Units (2022-2023): Complete logical viewport units (
dvi,dvb,svi,svb,lvi,lvb) with physical fallbacks - color-mix() Function (2021-2024): Advanced color mixing in different color spaces
- Scroll-driven Animations (2023-2024): Animations driven by scroll progress
- CSS Cascade Layers (2022): Better style organization with @layer
- Subgrid (2021-2023): Grid items participating in parent grid
- aspect-ratio Property (2021): Native aspect ratio control
- Enhanced Math Functions (2021-2023): clamp(), round(), trigonometric functions
📱 Responsive & Modern Layout
- CSS Anchor Positioning (2024): Position elements relative to other elements
- View Transitions (2023-2024): Smooth page/view transitions
- Enhanced Logical Properties: Complete writing-mode aware spacing, sizing, and positioning
- Container Style Queries: Query container's computed style values
- Container Scroll State Queries: Query container's scroll state
- Masonry Layout (Experimental): Pinterest-style layouts
🎨 Visual & Color Enhancements
- accent-color: Customize form control colors
- color-scheme: Light/dark mode indication
- light-dark() Function: Theme-aware color values
- backdrop-filter: Glass morphism effects
- conic-gradient: Conical gradients for complex designs
- corner-shape (Experimental): Superellipse curves for organic, Apple-like rounded corners
Automated Update Commands
# Discover and integrate new CSS features from MDN
npm run update-features
# Run feature discovery (development)
npm run discover-features
MDN Setup
- Uses direct MDN parsing with caching and structured extraction
- No external MCP dependencies required for documentation lookups
🌍 Logical Units & Internationalization
This MCP implements a logical-first approach to CSS suggestions, prioritizing writing-mode aware properties for better internationalization support.
Logical Units Priority System
Viewport Units (Logical Preferred)
dvi,dvb(dynamic viewport inline/block) →dvw,dvh(physical fallback)svi,svb(small viewport inline/block) →svw,svh(physical fallback)lvi,lvb(large viewport inline/block) →lvw,lvh(physical fallback)
Container Query Units (Logical Preferred)
cqi,cqb(container query inline/block) →cqw,cqh(physical fallback)
CSS Properties (Logical Preferred)
inline-size,block-size→width,height(physical fallback)margin-inline,margin-block→margin-left/right,margin-top/bottompadding-inline,padding-block→padding-left/right,padding-top/bottomborder-inline,border-block→border-left/right,border-top/bottominset-inline,inset-block→left/right,top/bottom
Advanced Container Queries
Size-based Container Queries (Enhanced)
@container (inline-size > 30cqi) {
.component {
gap: 2cqi;
}
}
Style Queries (NEW)
@container style(--theme: dark) {
.card {
background: var(--dark-bg);
}
}
Scroll State Queries (NEW)
@container scroll-state(stuck: top) {
.header {
backdrop-filter: blur(10px);
}
}
Writing-Mode Awareness
- RTL Language Support: Logical properties automatically adapt to right-to-left languages
- Vertical Writing Modes: Properties work correctly with
writing-mode: vertical-rl - International Compatibility: Suggestions prioritize globally compatible approaches
License
MIT