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

Related MCP server: mdnlookup

Usage

After adding the configuration:

1. Restart your MCP client

2. 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 solve

• preferred_approach (optional): 'modern', 'compatible', or 'progressive'

• target_browsers (optional): Array of target browsers/versions

• project_context (optional): Project context (framework, existing CSS patterns, constraints) NEW

• include_analysis (optional): Include semantic analysis details in response NEW

• baseline (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 check

• include_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 for

• include_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 use

• user_consent (boolean): User consent to use this CSS property

• fallback_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

1. Semantic Intent Recognition: Advanced regex patterns analyze task descriptions to understand user intent (layout, animation, spacing, responsive, visual, interaction)

2. Project Context Analysis: Detects frameworks, CSS libraries, build tools, and constraints from project context string

3. MDN Integration:

   • Direct MDN parsing for property details and support data

   • Caching: 1-hour intelligent cache for performance

4. Intelligent Ranking: Scores suggestions based on:

   • Intent match relevance

   • Browser support level

   • Framework compatibility

   • User confidence multiplier

5. Context-Aware Recommendations: Provides framework-specific guidance and best practices

6. 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/bottom

• padding-inline, padding-block → padding-left/right, padding-top/bottom

• border-inline, border-block → border-left/right, border-top/bottom

• inset-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