ATAG MCP

An MCP (Model Context Protocol) server that provides guidance on ATAG 2.0 — the W3C Authoring Tool Accessibility Guidelines — to help authoring tool developers build more accessible software.

What is ATAG?

ATAG 2.0 defines how authoring tools (rich-text editors, CMSes, IDEs, website builders, etc.) should:

• Part A — Be accessible to authors with disabilities (the tool's own UI)
• Part B — Help authors produce accessible web content (alt text prompts, accessibility checkers, accessible templates, etc.)

Why this exists

ATAG 2.0 has been a W3C Recommendation since 2015, but adoption among authoring tools remains limited — partly because the guidance is easy to overlook at the moment design and implementation decisions are actually made. With more authoring tool features now being built with the help of AI coding assistants, this server puts the full spec within the assistant's reach: describe the feature you're working on (an image upload dialog, a rich-text toolbar, a template picker) and get back the actual success criteria that apply, rather than a half-remembered summary. The aim is to lower the cost of considering ATAG at all — the first step towards tools that support it.

The data is a static, hand-checked copy of the ATAG 2.0 spec — not fetched or generated at runtime — so answers stay faithful to the W3C source. A weekly workflow checks for upstream spec changes.

Tools

Setup

No local install required — add the config below and your MCP client will fetch the package automatically via npx.

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "atag-mcp": {
      "command": "npx",
      "args": ["-y", "atag-mcp"]
    }
  }
}

VS Code (Claude extension)

{
  "mcp": {
    "servers": {
      "atag-mcp": {
        "type": "stdio",
        "command": "npx",
        "args": ["-y", "atag-mcp"]
      }
    }
  }
}

Local development install

npm install
npm run build
# then point your config to dist/index.js directly

Usage examples

Ask Claude:

• "What ATAG criteria apply to an image insertion dialog?" → uses get-guidance
• "Show me all Level A criteria from Part B" → uses get-criteria-by-level
• "Explain guideline B.3.1" → uses get-guideline
• "What does 'editing-view' mean in ATAG?" → uses get-glossary-term
• "Search ATAG for keyboard access" → uses search-atag

Development

npm run dev          # Run server directly with tsx (no compile step)
npm test             # Run all tests
npm run test:watch   # Watch mode
npm run validate-data  # Validate data/atag.json structure
npm run check-updates  # Check if W3C spec has changed

Branching and commits

This project follows git flow with [Conventional Commits](https://www.conventionalco

... View full README on GitHub