W3C

You set up and run the W3C MCP Server to let AI assistants access official web standards data, including specifications, WebIDL, CSS properties, and HTML elements. This enables fast, governed queries across W3C, WHATWG, and IETF specifications with structured results.

How to use

Start the MCP server through your preferred MCP client and connect using the stdio (local) or http method shown in the configuration examples. You can discover specs, fetch WebIDL definitions, retrieve CSS properties, and obtain HTML element information for any supported specification. Use individual tools to list specs, get detailed spec data, search specs by query, fetch WebIDL interfaces, and access PWA-related specifications.

How to install

Prerequisites you need before installation:

• Node.js is installed on your system (recommended latest LTS).
• You have npm installed (comes with Node.js).

Install the MCP server globally so you can run it from any terminal:

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

Or run it directly without installation using npx:

npx @shuji-bonji/w3c-mcp

Configuration

Configure the MCP client in your workflow so it can start the W3C MCP Server as a sub-process. You will add the MCP server entry to your client’s configuration.

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

If your workflow uses Cursor for project-level MCP integration, add an identical config block under your Cursor settings.

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

Notes

Environment variables and advanced debugging can be enabled via your MCP client’s environment or by setting debug flags when launching the server. If you enable debug mode, you’ll see tool call arguments, timing details, and data loading performance.

Tools and endpoints shown in the server

The server exposes a set of tools to access and filter W3C data. You can list specifications, fetch details for a single spec, search by query, retrieve WebIDL interfaces, and access CSS and HTML element definitions, as well as PWA-related specifications and dependencies.

Troubleshooting

If you encounter startup issues, verify Node.js and npm versions, ensure the MCP command is accessible in your shell, and check that the environment allows network access for any http-based endpoints if you use remote data sources.

Available tools

list_w3c_specs

List W3C/WHATWG/IETF web specifications with optional filtering by organization, keyword, category, and limit.

get_w3c_spec

Retrieve detailed information about a specific web specification using its shortname.

search_w3c_specs

Search specifications by a query string with an optional limit.

get_webidl

Get WebIDL interface definitions for a given specification shortname.

list_webidl_specs

List all specifications that have WebIDL definitions available.

get_css_properties

Retrieve CSS property definitions from a specific specification or all specifications.

list_css_specs

List all CSS specifications that have property definitions available.

get_html_elements

Retrieve HTML element definitions from a specific specification or all specifications.

list_element_specs

List all specifications that have HTML element definitions available.

get_pwa_specs

Get all Progressive Web App related specifications, with an option to filter core specs.

get_spec_dependencies

Get dependency information for a specification by shortname.