W3C MCP Server

W3C MCP Server

日本語版 README

MCP Server for accessing W3C/WHATWG/IETF web specifications. Provides AI assistants with access to official web standards data including specifications, WebIDL definitions, CSS properties, and HTML elements.

Installation

npm install -g @shuji-bonji/w3c-mcp

Or use directly with npx:

npx @shuji-bonji/w3c-mcp

Configuration

Claude Desktop

Add to your Claude Desktop configuration file:

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json Windows: %APPDATA%\Claude\claude_desktop_config.json

{
	"mcpServers": {
		"w3c": {
			"command": "npx",
			"args": ["-y", "@shuji-bonji/w3c-mcp"]
		}
	}
}

Cursor

Add to your Cursor MCP settings (.cursor/mcp.json in your project or global settings):

{
	"mcpServers": {
		"w3c": {
			"command": "npx",
			"args": ["-y", "@shuji-bonji/w3c-mcp"]
		}
	}
}

Available Tools

Specification Discovery

`list_w3c_specs`

List W3C/WHATWG/IETF web specifications with optional filtering.

Parameters:

• organization (optional): Filter by organization - "W3C", "WHATWG", "IETF", or "all"
• keyword (optional): Filter by keyword in title or shortname
• category (optional): Filter by category
• limit (optional): Maximum number of results (default: 50)

`get_w3c_spec`

Get detailed information about a specific web specification.

Parameters:

• shortname (required): Specification shortname (e.g., "service-workers", "appmanifest", "fetch")

`search_w3c_specs`

Search web specifications by query string.

Parameters:

• query (required): Search query (e.g., "service worker", "manifest", "storage")
• limit (optional): Maximum number of results (default: 20)

WebIDL

`get_webidl`

Get WebIDL interface definitions for a specification. WebIDL defines the JavaScript APIs.

Parameters:

• shortname (required): Specification shortname (e.g., "service-workers", "fetch", "dom")

`list_webidl_specs`

List all specifications that have WebIDL definitions available.

CSS

`get_css_properties`

Get CSS property definitions from a specific spec or all specs.

Parameters:

• spec (optional): Specification shortname (e.g., "css-grid-1", "css-flexbox-1")
• property (optional): Search for a specific CSS property by name

`list_css_specs`

List all CSS specifications that have property definitions available.

HTML Elements

`get_html_elements`

Get HTML element definitions from a specific spec or all specs.

Parameters:

• spec (optional): Specification shortname (e.g., "html", "svg")
• element (optional): Search for a specific element by name (e.g., "video", "canvas")

`list_element_specs`

List all specifications that have HTML element definitions available.

PWA

`get_pwa_specs`

Get all Progressive Web App (PWA) related specifications.

Parameters:

• coreOnly (optional): If true, return only the core PWA specs (Service Worker, Manifest, Push, Notifications)

`get_spec_dependencies`

Get dependency information for a specification.

Parameters:

• shortname (required): Specification shortname

Usage Examples

Find Service Worker APIs

Use the get_webidl tool with shortname "service-workers" to see the ServiceWorker interface definitions.

Explore PWA Technologies

Use get_pwa_specs to see all PWA-related specifications, then use get_w3c_spec for details on each one.

Look up CSS Grid Properties

Use get_css_properties with spec "css-grid-1" to see all CSS Grid layout properties.

Search for Storage APIs

Use search_w3c_specs with query "storage" to find all storage-related specifications.

Data Sources

This MCP server uses the following W3C/webref data packages: