WCAG Accessibility MCP

A WCAG accessibility testing MCP for AI agents, Codex, Claude Code, and automated UI audits.

WCAG Accessibility MCP gives AI coding and design agents a real accessibility feedback loop. It renders web interfaces in Chromium, runs axe-core, checks color contrast, maps findings to WCAG guidance, and returns structured evidence that an agent can use to fix accessibility issues before a UI is treated as complete.

It is designed for people building with AI: product designers, design engineers, frontend developers, AI product teams, and anyone using agents to generate or review web interfaces.

This is an automated testing aid, not a WCAG certification service. It catches many common failures, but full accessibility review still requires human testing for keyboard behavior, focus order, screen readers, zoom, motion, content quality, and assistive-technology behavior.

Why This Exists

AI-generated interfaces often look polished but fail basic accessibility checks: weak contrast, missing labels, broken semantic structure, poor ARIA usage, inaccessible forms, and hidden keyboard issues.

This MCP helps agents stop guessing. Instead of saying “follow WCAG,” it gives them testable feedback:

• what failed
• where it failed
• which element was affected
• which WCAG-related rule applies
• what needs to be fixed
• which checks still require manual review

What It Can Do

Tool	What it does
audit_url	Audits a rendered web page URL
audit_html	Audits supplied HTML before it is hosted
audit_file	Audits a local .html or .htm file inside an allowed project root
audit_matrix	Experimental: audits one target across named viewports and groups findings by stable fingerprints
compare_audits	Experimental: compares baseline and candidate audit results without rerunning the browser
browser_diagnostics	Experimental: reports browser selection and setup guidance without launching Chromium
inspect_screenshot	Experimental: captures screenshot evidence and optionally runs local OCR
inspect_design_snapshot	Experimental: inspects exported Figma, Claude Design, or generic design-node data before implementation
check_contrast	Calculates WCAG contrast for a foreground/background color pair
suggest_contrast_fix	Suggests a passing color adjustment
explain_issue	Explains an accessibility rule and how to fix it
get_wcag_checklist	Returns the complete WCAG checklist with automated/manual coverage

Standards Coverage

The server supports these profiles:

• wcag2a
• wcag2aa
• wcag2aaa
• wcag21aa
• wcag21aaa
• wcag22aa
• wcag22aaa
• best-practice

AA profiles include Level A and AA criteria. AAA profiles include Level A, AA, and AAA criteria.

The default profile is wcag22aa.

For WCAG 2.2:

• AA includes 55 required success criteria.
• AAA includes 86 required success criteria.

An automated axe mapping means partial automated coverage. It does not mean the whole WCAG success criterion has been fully tested.

Install

Requirements:

• Node.js 20 or newer
• Chrome or Edge recommended
• Windows, macOS, or Linux

Install from npm:

npm install -g wcag-accessibility-mcp

Or run directly:

npx -y wcag-accessibility-mcp

If the server starts correctly, you should see:

wcag-accessibility-mcp is running over stdio

Use With Claude Code

Add the MCP server:

claude mcp add --scope user wcag-accessibility -- npx -y wcag-accessibility-mcp

Check that it is connected:

claude mcp list

Test prompt:

Use the wcag-accessibility MCP tool check_contrast. Check #999999 on #ffffff for WCAG AA normal text. Do not calculate manually.

Expected result:

The contrast ratio is about 2.85:1, which fails WCAG AA for normal text.

Use With Claude Desktop

Open the Claude desktop config file on Windows:

notepad "$env:APPDATA\Claude\claude_desktop_config.json"

Add this inside mcpServers:

{
  "mcpServers": {
    "wcag-accessibility": {
      "command": "C:\\Program Files\\nodejs\\npx.cmd",
      "args": [
        "-y",
        "wcag-accessibility-mcp"
      ]
    }
  }
}

If you already have another MCP server, keep it and add wcag-accessibility as a second entry.

Then fully quit Claude Desktop and reopen it.

Use With Codex

Add the MCP server:

codex mcp add wcag-accessibility -- npx -y wcag-accessibility-mcp

Test prompt:

Use the wcag-accessibility MCP to check the contrast of #999999 on #ffffff at WCAG AA.

Example Agent Prompts

Audit this HTML for WCAG 2.2 AA issues. Prioritize critical and serious issues, explain each fix, then list what still needs manual review.

Use wcag-accessibility to audit this local HTML file at desktop and mobile widths. Fix the accessibility issues in the code and rerun the audit.

Inspect this Figma or Claude Design snapshot for accessibility risks before implementation, then verify the rendered HTML with audit_matrix.

Capture a screenshot of this page and run OCR only if local OCR is configured. Use OCR findings as visual evidence, not as WCAG conformance.

Check whether #FF3B12 on #F5F2EC passes WCAG AA for normal text. If it fails, suggest the nearest passing foreground color.

Give me the WCAG 2.2 AAA checklist and separate automated checks from manual checks.

Local Development

Clone the repository:

git clone https://github.com/aditya-ariosity/wcag-accessibility-mcp.git
cd wcag-accessibility-mcp

Install dependencies:

npm install

Build:

npm run build

Run tests:

npm run test:unit

Run browser integration and end-to-end tests:

npm run test:browser

npm test is the deterministic browser-free unit suite. Use npm run test:browser when the machine has a working Chrome, Edge, Chromium, or bundled browser setup.

The CLI can write JSON, Markdown, or SARIF reports and compare a baseline:

npm run audit -- --url http://localhost:3000 --format json --out report.json
npm run audit -- --url http://localhost:3000 --baseline baseline.json --format md

Start the stdio MCP server:

npm start

Start the optional HTTP transport:

npm run start:http

The local HTTP endpoint is:

http://127.0.0.1:3000/mcp

Health check:

http://127.0.0.1:3000/health

Environment Variables

All environment variables are optional for normal local use.

Variable	Default	Purpose
A11Y_MCP_BROWSER_PATH	Auto-detected	Absolute path to Chrome, Chromium, or Edge
A11Y_MCP_ALLOWED_ROOT	Current working directory	Restricts local file audits to a specific folder
A11Y_MCP_ALLOW_PRIVATE	true on stdio, false on HTTP	Allows localhost/private-network URL audits in trusted environments
A11Y_MCP_ENABLE_FILE_AUDIT	false on HTTP	Enables local file audits over HTTP in trusted deployments
A11Y_MCP_BROWSER_CONCURRENCY	2	Maximum concurrent Chromium audits
A11Y_MCP_AUDIT_TIMEOUT_MS	25000	Timeout for the audit phase
A11Y_MCP_NO_SANDBOX	false	Disables Chromium sandboxing only when the runtime requires it
A11Y_MCP_OCR_COMMAND	tesseract	Local OCR executable used by inspect_screenshot when runOcr is true
A11Y_MCP_ENABLE_EXPERIMENTAL_TOOLS	false	Advertises the in-progress matrix, screenshot, diagnostics, and design-snapshot tools
A11Y_MCP_ALLOW_LOCAL_FILE_SUBRESOURCES	false	Allows local file audits to load file-based images/stylesheets beneath the allowed root
HOST / A11Y_MCP_HOST	127.0.0.1	HTTP bind address
A11Y_MCP_ALLOWED_HOSTS	Localhost names	Allowed Host headers for HTTP mode
A11Y_MCP_BODY_LIMIT	4mb	HTTP JSON body limit
PORT	3000	HTTP transport port

Security Notes

The stdio server is meant to run locally with the same permissions as the agent using it.

The HTTP transport is a deployment building block, not a public hosted service by itself. Do not expose it directly to the public internet without authentication, TLS, rate limits, request-size limits, outbound network controls, and a low-privilege runtime.

By default:

• tools are read-only
• HTTP mode blocks private network URL targets
• local file audit over HTTP is disabled
• local file audit is restricted to the allowed root
• Chromium sandboxing remains enabled unless explicitly disabled

Published Links

• GitHub: https://github.com/aditya-ariosity/wcag-accessibility-mcp
• npm: https://www.npmjs.com/package/wcag-accessibility-mcp
• MCP Registry name: io.github.aditya-ariosity/wcag-accessibility

Current Scope

The stable release currently audits rendered web interfaces and HTML. The evidence core reports criterion-level coverage and keeps unresolved manual requirements visible.

The stable release does not yet inspect:

• native mobile apps
• PDFs
• canvas-only interfaces
• video captions
• raw screenshots without HTML
• raw Claude Design pixels

Matrix, screenshot/OCR, and design-snapshot modules are experimental and require A11Y_MCP_ENABLE_EXPERIMENTAL_TOOLS=true. Direct Figma plugin inspection, persistence, automatic fixes, and deeper design-tool adapters remain future work.

License

MIT