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Accessibility MCP Server

by Duds
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Accessibility MCP Server

An MCP (Model Context Protocol) server that provides accessibility auditing tools for LLMs through Cursor. Integrates axe-core (via Playwright), Lighthouse CLI, and optional WAVE API to deliver deterministic, machine-actionable accessibility audit results.

Features

  • axe-core Integration: Automated accessibility testing via Playwright with full WCAG 2.1/2.2 coverage

  • Lighthouse CLI: Comprehensive accessibility audits with performance insights

  • WAVE API: Optional integration for additional accessibility validation

  • Deterministic Output: All results normalised to explicit pass/fail/unknown outcomes

  • WCAG Compliance: Every finding mapped to WCAG 2.1/2.2 criteria with severity classification

  • Machine-Actionable: Results include selectors and DOM context for remediation

  • Type-Safe: Full TypeScript implementation with strict type checking

Installation

# Clone the repository git clone <repository-url> cd accessibility-mcp # Install dependencies npm install # Build the project npm run build # Install Playwright browsers (required for axe-core) npx playwright install chromium

Configuration

Create a .env file in the project root (see .env.example for template):

# WAVE API Configuration (optional) WAVE_API_KEY=your_wave_api_key_here WAVE_API_URL=https://wave.webaim.org/api/request # Lighthouse Configuration (optional) LIGHTHOUSE_TIMEOUT=60000 LIGHTHOUSE_CHROME_FLAGS=--headless --no-sandbox # Playwright Configuration (optional) PLAYWRIGHT_BROWSER=chromium PLAYWRIGHT_TIMEOUT=30000

Usage

As MCP Server in Cursor

  1. Build the project: npm run build

  2. Configure in Cursor's MCP settings (~/.cursor/mcp.json or Cursor settings):

{ "mcpServers": { "accessibility": { "command": "node", "args": ["/absolute/path/to/accessibility-mcp/dist/index.js"] } } }

  1. Restart Cursor to load the MCP server

Available MCP Tools

axe_audit

Run an accessibility audit using axe-core via Playwright. Supports URLs, local file paths, and localhost URLs.

Parameters:

  • url (required): The URL to audit. Can be:

    • HTTP/HTTPS URL: "https://example.com" or "http://localhost:3000"

    • Local file path: "./index.html" or "/path/to/file.html"

    • File protocol URL: "file:///path/to/file.html"

  • options (optional): Configuration object

    • tags: Array of WCAG tags (e.g., ["wcag2a", "wcag2aa"])

    • rules: Object with rule-specific configuration

    • timeout: Timeout in milliseconds (default: 30000)

    • browser: Browser to use - "chromium", "firefox", or "webkit" (default: "chromium")

Examples:

{ "name": "axe_audit", "arguments": { "url": "https://example.com", "options": { "tags": ["wcag2a", "wcag2aa"], "browser": "chromium" } } }
{ "name": "axe_audit", "arguments": { "url": "./src/index.html" } }
{ "name": "axe_audit", "arguments": { "url": "http://localhost:3000" } }

lighthouse_audit

Run an accessibility audit using Lighthouse CLI. Supports URLs, local file paths, and localhost URLs.

Parameters:

  • url (required): The URL to audit. Can be:

    • HTTP/HTTPS URL: "https://example.com" or "http://localhost:3000"

    • Local file path: "./index.html" or "/path/to/file.html"

    • File protocol URL: "file:///path/to/file.html"

  • categories (optional): Array of Lighthouse categories to include

  • options (optional): Configuration object

    • onlyCategories: Array of categories to include

    • skipAudits: Array of audit IDs to skip

    • timeout: Timeout in milliseconds (default: 60000)

Examples:

{ "name": "lighthouse_audit", "arguments": { "url": "https://example.com", "categories": ["accessibility"] } }
{ "name": "lighthouse_audit", "arguments": { "url": "./dist/index.html" } }

wave_audit

Run an accessibility audit using WAVE API (requires API key). Supports URLs and localhost URLs. Local files are automatically served via a temporary local server.

Parameters:

  • url (required): The URL to audit. Can be:

    • HTTP/HTTPS URL: "https://example.com" or "http://localhost:3000"

    • Local file path: "./index.html" (will be served via temporary server)

  • apiKey (optional): WAVE API key (uses WAVE_API_KEY env var if not provided)

Examples:

{ "name": "wave_audit", "arguments": { "url": "https://example.com", "apiKey": "your_api_key" } }
{ "name": "wave_audit", "arguments": { "url": "./src/index.html" } }

Note: For local files, the MCP server automatically creates a temporary HTTP server to serve the file, as WAVE API requires HTTP/HTTPS URLs.

Output Format

All tools return normalised results in the following format:

{ url: string; tool: 'axe' | 'lighthouse' | 'wave'; timestamp: string; results: Array<{ rule_id: string; wcag_ref: string[]; severity: 'critical' | 'serious' | 'moderate' | 'minor'; confidence: 'high' | 'medium' | 'low'; outcome: 'pass' | 'fail' | 'unknown'; selector: string; dom_context: string; message: string; reason_code?: string; // Required when outcome is 'unknown' }>; summary: { total: number; pass: number; fail: number; unknown: number; by_severity: { critical: number; serious: number; moderate: number; minor: number; }; }; }

Development

Prerequisites

  • Node.js 18.0.0 or higher

  • npm or yarn

Scripts

# Development mode (with hot reload) npm run dev # Build TypeScript to JavaScript npm run build # Run all tests npm test # Run unit tests only npm run test:unit # Run integration tests only npm run test:integration # Type check without building npm run type-check # Lint code npm run lint

Project Structure

accessibility-mcp/ ├── .cursor/ │ ├── rules/ # Cursor behavioural constraints │ └── commands/ # Cursor repeatable actions ├── src/ │ ├── adapters/ # External tool adapters (axe, Lighthouse, WAVE) │ ├── services/ # Business logic (audits, normalisation) │ ├── tools/ # MCP tool definitions │ ├── types/ # TypeScript type definitions │ ├── utils/ # Utility functions (WCAG mappings, selectors) │ ├── index.ts # Entry point │ └── server.ts # MCP server setup ├── tests/ │ ├── fixtures/ # Test data fixtures │ ├── unit/ # Unit tests │ └── integration/ # Integration tests └── dist/ # Compiled JavaScript output

Architecture

The server follows a clean architecture pattern:

  1. Tools Layer (src/tools/): MCP tool definitions that expose audit capabilities

  2. Services Layer (src/services/): Business logic for audit execution and result normalisation

  3. Adapters Layer (src/adapters/): Interface layer for external tools (axe, Lighthouse, WAVE)

  4. Types Layer (src/types/): Shared type definitions for audit results and normalised outputs

Adding a New Audit Tool

See .cursor/commands/add-new-audit-tool.md for detailed instructions on adding a new accessibility audit tool.

Testing

# Run all tests npm test # Run with coverage npm test -- --coverage # Run specific test file npm test tests/unit/normaliser.test.ts

CI/CD Integration

The project includes commands for CI/CD integration. See .cursor/commands/ci-gate-accessibility.md for details on setting up accessibility gates in your CI pipeline.

Contributing

  1. Follow the architectural constraints defined in .cursor/rules/

  2. Ensure all code passes type checking: npm run type-check

  3. Write tests for new features

  4. Ensure deterministic outputs (see .cursor/rules/determinism.md)

  5. Map all findings to WCAG criteria (see .cursor/rules/accessibility.md)

License

MIT

Acknowledgments

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