CSS MCP Server

Universal CSS Analysis and Documentation MCP Server. Analyze any CSS with ~150 derived metrics (built on ~78 CSSMetrics fields plus selector/property counters) for complexity, specificity, and quality.

Features

• CSS Analysis: ~150 derived metrics (78 CSSMetrics fields plus selector/property counters) for CSS complexity, specificity, and quality
• MDN Documentation: Fetch CSS property docs from MDN Web Docs
• Browser Compatibility: Check cross-browser support for CSS properties
• Project Analysis: Analyze all CSS files in a project

Installation

# Using uv
uv pip install css-mcp

# Using pip
pip install css-mcp

Usage

Start Server

# Via CLI
css-mcp

# Via Python module
python -m css_mcp.server

Environment Variables

Available Tools

Programmatic Usage

Use the analyzer directly in Python for any CSS:

Example: Analyze Any CSS

from css_mcp.analyzer import CSSAnalyzer

# Analyze any CSS content
analyzer = CSSAnalyzer()
metrics = analyzer.analyze(css_content)

# Get complexity score
print(f"Complexity: {metrics.complexity_score}/100")

# Get optimization suggestions
suggestions = analyzer.get_suggestions()

Metrics

The analyzer provides ~150 derived metrics (built from 78 CSSMetrics fields plus selector and property counters), including:

Basic Metrics

• Total rules, selectors, properties
• File size (bytes, gzipped)
• Lines of code

Selector Metrics

• ID, class, element, universal selectors
• Pseudo-classes and pseudo-elements
• Combinators (descendant, child, sibling)
• Selector depth

Specificity Metrics

• Average, min, max specificity
• High specificity rules
• Specificity distribution

Property Metrics

• Unique properties
• Category distribution (layout, typography, etc.)
• Vendor prefixes
• !important usage
• CSS custom properties

Quality Metrics

• Duplicate selectors
• Duplicate properties
• Empty rules
• Complexity score
• Efficiency scores

Browser Compatibility

Built-in compatibility data for common CSS properties across:

• Chrome
• Firefox
• Safari
• Edge

Development

# Install dev dependencies
uv sync --group dev

# Run tests
pytest

# Type check
mypy css_mcp

# Lint
ruff check css_mcp

Installation via Claude Code marketplace

The css plugin is published through the www-mcp-servers marketplace. Register the marketplace once, install the plugin, and the css-mcp HTTP server becomes available as mcp__css__* tools alongside three slash commands (/css-audit-project, /css-analyze, /css-check-compat). The plugin manifest lives at .claude-plugin/plugin.json and the server is registered in the colocated .mcp.json at http://localhost:3050/mcp — start the css-mcp server first, then run claude plugin install css --marketplace www-mcp-servers from a fresh session.

License

BSD-3-Clause

Built on Oneiric for runtime configuration and mcp-common for the FastMCP baseline. Crackerjack gates every commit.