Web Accessibility-Testing MCP Server (A11y MCP)

A11y MCP is an MCP (Model Context Protocol) server that gives LLMs access to web accessibility testing APIs.

This server uses the Deque Axe-core API and Puppeteer to allow LLMs to analyze web content for WCAG compliance and identify accessibility issues.

NOTE: This is not an official MCP server from Deque Labs.

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Features

• Test web pages: Test any public URL for accessibility issues
• Test HTML snippets: Test raw HTML strings for accessibility issues
• WCAG compliance testing: Check content against various WCAG standards (2.0, 2.1, 2.2)
• Customizable tests: Specify which accessibility tags/standards to test against
• Rule exploration: Get information about available accessibility rules
• Color contrast analysis: Check color combinations for WCAG compliance
• ARIA validation: Test proper usage of ARIA attributes
• Orientation lock detection: Identify content that forces specific screen orientations

Installation

To use this server with Claude Desktop, you need to configure it in the MCP settings:

For macOS: Edit the file at '~/Library/Application Support/Claude/claude_desktop_config.json'

{
  "mcpServers": {
    "a11y-accessibility": {
    "command": "npx",
    "args": [
      "-y",
      "a11y-mcp-server"
    ]
   }
  }
}

For Windows: Edit the file at %APPDATA%\Claude\settings\claude_mcp_settings.json

For Linux: Edit the file at ~/.config/Claude/settings/claude_mcp_settings.json Replace /path/to/axe-mcp-server/build/index.js with the actual path to your compiled server file.

Available Tools

test_accessibility

Tests a URL for accessibility issues.

Parameters:

• url (required): The URL of the web page to test
• tags (optional): Array of WCAG tags to test against (e.g., ["wcag2aa"])

Example

{
 "url": "https://example.com",
 "tags": ["wcag2aa"]
}

test_html_string

Tests an HTML string for accessibility issues. Parameters:

• html (required): The HTML content to test
• tags (optional): Array of WCAG tags to test against (e.g., ["wcag2aa"])

Example

{
  "html": "",
  "tags": ["wcag2aa"]
}

get_rules

Get information about available accessibility rules with optional filtering.

check_color_contrast

Check if a foreground and background color combination meets WCAG contrast requirements.

Parameters:

• foreground (required): Foreground color in hex format (e.g., "#000000")
• background (required): Background color in hex format (e.g., "#FFFFFF")
• fontSize (optional): Font size in pixels (default: 16)
• isBold (optional): Whether the text is bold (default: false)

Example

{
  "foreground": "#777777",
  "background": "#EEEEEE",
  "fontSize": 16,
  "isBold": false
}

check_color_contrast

Check if ARIA attributes are used correctly in HTML.

Parameters:

• html (required): HTML content to test for ARIA attribute usage

Example

{
  "html": "Click me"
}

check_orientation_lock

Check if content forces a specific orientation.

Parameters:

• html (required): HTML content to test for orientation lock issues

Example

{
  "html": "Content"
}

Response Format

The server returns accessibility test results in a structured JSON format:

{
  "violations": [
    {
      "id": "color-contrast",
      "impact": "serious",
      "description": "Ensure the contrast between foreground and background colors meets WCAG 2 AA minimum contrast ratio thresholds",
      "help": "Elements must meet minimum color contrast ratio thresholds",
      "helpUrl": "https://dequeuniversity.com/rules/axe/4.10/color-contrast",
      "affectedNodes": [
        {
          "html": "Low contrast text",
          "target": ["div"],
          "failureSummary": "Fix any of the following: Element has insufficient color contrast of 1.98 (foreground color: #aaa, background color: #eee, font size: 12.0pt, font weight: normal)"
        }
      ]
    }
  ],
  "passes": 1,
  "incomplete": 0,
  "inapplicable": 2,
  "timestamp": "2025-04-25T16:45:33.655Z",
  "url": "about:blank",
  "testEngine": {
    "name": "axe-core",
    "version": "4.10.3"
  },
  "testRunner": {
    "name": "axe"
  },
  "testEnvironment": {
    "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/135.0.0.0 Safari/537.36",
    "windowWidth": 800,
    "windowHeight": 600,
    "orientationAngle": 0,
    "orientationType": "portrait-primary"
  }
}

Dependencies

• @modelcontextprotocol/sdk
• puppeteer
• @axe-core/puppeteer
• axe-core

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