# W3c Mcp

> 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.

- **Type:** MCP server
- **Install:** `agentstack add mcp-shuji-bonji-w3c-mcp`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [shuji-bonji](https://agentstack.voostack.com/s/shuji-bonji)
- **Installs:** 0
- **Category:** [Integrations](https://agentstack.voostack.com/c/integrations)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [shuji-bonji](https://github.com/shuji-bonji)
- **Source:** https://github.com/shuji-bonji/w3c-mcp
- **Website:** https://www.npmjs.com/package/@shuji-bonji/w3c-mcp

## Install

```sh
agentstack add mcp-shuji-bonji-w3c-mcp
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# W3C MCP Server

[](https://www.npmjs.com/package/@shuji-bonji/w3c-mcp)
[](https://opensource.org/licenses/MIT)
[](https://nodejs.org/)
[](https://modelcontextprotocol.io/)
[](https://claude.ai/code)

[日本語版 README](README.ja.md)

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

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

Or use directly with npx:

```bash
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`
**Linux**: `~/.config/Claude/claude_desktop_config.json`

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

### Claude Code

Add the server using the `claude mcp` CLI:

```bash
claude mcp add w3c -- npx -y @shuji-bonji/w3c-mcp
```

Or edit `~/.claude.json` / project-level `.mcp.json` manually with the same `mcpServers` block shown above.

### Cursor

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

```json
{
  "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 basic information for a specification.

> **Note**: Dependency data (`dependencies` / `dependents`) is not yet exposed by the upstream [`web-specs`](https://www.npmjs.com/package/web-specs) package, so these fields currently return empty arrays. Only the base spec metadata is reliable for now.

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:

| Package                                                            | Description                         |
| ------------------------------------------------------------------ | ----------------------------------- |
| [web-specs](https://www.npmjs.com/package/web-specs)               | Metadata for all web specifications |
| [@webref/idl](https://www.npmjs.com/package/@webref/idl)           | WebIDL interface definitions        |
| [@webref/css](https://www.npmjs.com/package/@webref/css)           | CSS properties and values           |
| [@webref/elements](https://www.npmjs.com/package/@webref/elements) | HTML element definitions            |

These packages are maintained by the W3C and provide machine-readable data extracted from official specifications.

**GitHub Repositories**:

- https://github.com/w3c/browser-specs
- https://github.com/w3c/webref

## Debug Mode

Enable debug logging with environment variables:

```bash
# Enable debug logging
W3C_MCP_DEBUG=true npx @shuji-bonji/w3c-mcp

# Enable performance logging only
W3C_MCP_PERF=true npx @shuji-bonji/w3c-mcp
```

Debug output includes:

- Tool call arguments
- Execution timing
- Data loading performance

## Architecture

```
src/
├── index.ts           # MCP server entry point
├── constants/
│   └── index.ts       # Centralized configuration constants
├── data/
│   └── loader.ts      # Data loading with caching
├── tools/             # Tool implementations
│   ├── list-specs.ts
│   ├── get-spec.ts
│   ├── search-specs.ts
│   ├── get-webidl.ts
│   ├── get-css.ts
│   ├── get-elements.ts
│   └── get-pwa-specs.ts
├── schemas/
│   └── index.ts       # Zod validation schemas
├── errors/
│   └── index.ts       # Custom error classes
├── utils/
│   ├── logger.ts      # Debug logging utilities
│   ├── mapper.ts      # Spec data mapping utilities
│   ├── search.ts      # Generic search utilities
│   └── suggestions.ts # Suggestion generation utilities
└── types/
    └── index.ts       # TypeScript type definitions

tests/
├── setup.ts           # Test setup
├── data/              # Data loader tests
├── tools/             # Tool tests
└── integration/       # MCP server integration tests
```

### Performance

- **Startup**: ~70ms parallel preloading of all data
- **Spec Lookup**: O(1) using Map-based index
- **Search**: Optimized with early termination on exact matches

## Development

```bash
# Clone the repository
git clone https://github.com/shuji-bonji/w3c-mcp.git
cd w3c-mcp

# Install dependencies
npm install

# Build
npm run build

# Run in development mode
npm run dev

# Run with debug logging
W3C_MCP_DEBUG=true npm start

# Run tests
npm test

# Run tests with coverage
npm run test:coverage

# Lint code
npm run lint

# Format code
npm run format

# Lint + format (auto-fix)
npm run check
```

## License

MIT

## Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [shuji-bonji](https://github.com/shuji-bonji)
- **Source:** [shuji-bonji/w3c-mcp](https://github.com/shuji-bonji/w3c-mcp)
- **License:** MIT
- **Homepage:** https://www.npmjs.com/package/@shuji-bonji/w3c-mcp

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/mcp-shuji-bonji-w3c-mcp
- Seller: https://agentstack.voostack.com/s/shuji-bonji
- Browse the marketplace: https://agentstack.voostack.com/browse

---
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