accessibility-mcp-server

MCP-Server for Web Accessibility Checks (WCAG 2.1/2.2)

Gives AI agents the ability to check websites for accessibility issues, validate ARIA attributes, check color contrast ratios, and generate full accessibility reports — without any API key.

Features

• WCAG 2.1 AA Compliance Checks — Automated checks for 10+ WCAG success criteria
• Color Contrast Analyzer — Calculates contrast ratios and WCAG AA/AAA pass/fail
• ARIA Validator — Checks ARIA roles and attributes for correctness
• Heading Structure Analyzer — Validates heading hierarchy (H1→H2→H3...)
• Image Alt Text Checker — Finds images missing alt attributes
• Form Label Validator — Ensures all form inputs have accessible labels
• Full A11y Report — Comprehensive report with accessibility score (0-100)
• WCAG Rule Reference — Browse all WCAG 2.1 A/AA/AAA rules
• No API Key Required — Works with any public website

Tools

Tool	Description
check_url_accessibility	Full WCAG 2.1 AA check for any URL
check_color_contrast	Calculate contrast ratio between two colors
validate_aria	Validate ARIA attributes in HTML snippet
check_heading_structure	Analyze heading hierarchy on a page
check_images_alt	Check all images for alt text
check_form_labels	Check all form inputs for labels
generate_a11y_report	Comprehensive accessibility report with score
list_wcag_rules	List all WCAG 2.1 rules for a given level

Installation

pip install accessibility-mcp-server

Usage with Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "accessibility": {
      "command": "accessibility-mcp-server"
    }
  }
}

Example Prompts

• "Check https://example.com for accessibility issues"
• "What is the contrast ratio between #333333 and #ffffff?"
• "Generate a full accessibility report for https://mysite.com"
• "Check if the images on https://example.com have alt text"
• "Validate the ARIA in this HTML: <div role='buttn'>Click</div>"
• "List all WCAG 2.1 AA rules"

WCAG Criteria Checked

Criterion	Level	Check
1.1.1 Non-text Content	A	Images without alt text
1.3.1 Info and Relationships	A	Heading hierarchy, landmark regions
1.4.3 Contrast (Minimum)	AA	Color contrast ratio calculator
2.4.1 Bypass Blocks	A	Skip links and landmarks
2.4.2 Page Titled	A	Missing or empty page titles
2.4.4 Link Purpose	A	Generic link text detection
3.1.1 Language of Page	A	Missing lang attribute
3.3.2 Labels or Instructions	A	Form inputs without labels
4.1.1 Parsing	A	Duplicate IDs
4.1.2 Name, Role, Value	A	ARIA validation, unlabeled buttons

Tech Stack

• Python 3.10+ with FastMCP
• httpx for async HTTP requests
• BeautifulSoup4 + lxml for HTML parsing
• WCAG formulas implemented directly (relative luminance, contrast ratio)

License

MIT — Free for personal and commercial use.

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Built by AiAgentKarl | Part of the AI Agent Tools ecosystem