A11y Expert MCP

An accessibility expert for your AI coding assistant. This MCP (Model Context Protocol) server gives AI tools like Claude, Cursor, and Windsurf real-time access to WAI-ARIA patterns, code review, contrast checking, and WCAG guidance — so the code they write is accessible from the start.

What's Inside

🔧 Tools

Tool	What it does
get_pattern	Get the full WAI-ARIA implementation pattern for any UI component — roles, states, keyboard interaction, and code examples.
review_code	Paste HTML/JSX/TSX/Vue/Svelte code and get a list of accessibility issues with specific fixes and WCAG references. Detects 10+ anti-patterns including missing labels, click-on-divs, broken heading hierarchy, missing dialog roles, and more.
list_patterns	See all 33 component patterns available in the knowledge base.
check_contrast	Check any two hex colors against WCAG AA and AAA contrast requirements for both normal and large text.

📚 Knowledge Base (33 Components)

Every pattern comes from the WAI-ARIA Authoring Practices and includes roles, states, properties, keyboard interaction, and code examples.

Canonical source: The 33 pattern instruction files in this server are synced from a11y-skills, the community-maintained source of truth. If you want to contribute a new pattern or improve an existing one, open the PR there.

Accordion	Alert	Alert Dialog	Breadcrumbs
Buttons	Carousel	Checkbox	Combobox
Dialog (Modal)	Disclosure	Feed	Grid
Headings	Image Labeling	Landmarks	Link
Listbox	Menu	Menu Button	Meter
Radio	Slider	Slider (Multi-thumb)	Spinbutton
Switch	Tables	Tabs	Toolbar
Tooltip	Treeview	Treegrid	Window Splitter
Accessibility (General)

💬 Prompts

Pre-built workflows your AI assistant can use:

Prompt	What it does
audit-component	Step-by-step accessibility audit — checks ARIA, keyboard, focus, contrast, headings, touch targets. Provide code + optional component type.
make-accessible	Rewrites inaccessible code into a fully accessible implementation with WAI-ARIA patterns and comments explaining every change.
check-form-accessibility	Form-specific audit — labels, required fields, error handling, fieldsets, autocomplete, tab order, and submit feedback.
wcag-checklist	Generates a WCAG 2.2 compliance checklist (AA or AAA) organized by principle, tailored to your page or component.
aria-guide	Complete ARIA implementation guide for a component — roles, attributes, keyboard table, focus management, screen reader script, and code example.

📖 Resources

Browsable knowledge base for MCP clients:

• a11y://patterns — Index of all 33 component patterns
• a11y://patterns/{component} — Full pattern detail for any component

Installation

Prerequisites

• Python 3.11+
• uv (recommended) or pip

Option 1: Run directly with uvx (no install needed)

uvx a11y-expert-mcp

Option 2: Install with pip

pip install a11y-expert-mcp

Then run:

a11y-expert-mcp

Option 3: Run from source

git clone https://github.com/Elizabeth1979/a11y-expert-mcp.git
cd a11y-expert-mcp
uv run a11y-expert-mcp

Configuration

Claude Desktop / Claude Code

Add to your MCP config (~/.claude/config.json or Claude Desktop settings):

{
  "mcpServers": {
    "a11y": {
      "command": "uvx",
      "args": ["a11y-expert-mcp"]
    }
  }
}

Or if running from source:

{
  "mcpServers": {
    "a11y": {
      "command": "uv",
      "args": [
        "run",
        "--project",
        "/path/to/a11y-expert-mcp",
        "a11y-expert-mcp"
      ]
    }
  }
}

Cursor / Windsurf / Other MCP Clients

Use the same command and args — check your editor's MCP configuration docs for the exact config file location.

Usage Examples

Once connected, your AI assistant can:

Get an accessible pattern:

"How do I build an accessible tabs component?" → The assistant calls get_pattern("tabs") and gets the full WAI-ARIA pattern with keyboard interaction and code.

Review code for issues:

"Check this modal for accessibility problems" → The assistant calls review_code(code, component_type="modal") and gets specific issues with fixes.

Check color contrast:

"Does #666 on #fff pass WCAG?" → The assistant calls check_contrast("#666", "#fff") and gets AA/AAA results for normal and large text.

Generate a WCAG checklist:

"Give me a WCAG AA checklist for my checkout page" → The assistant uses the wcag-checklist prompt to generate a tailored compliance checklist.

How It Works

The server bundles 33 WAI-ARIA pattern documents as a knowledge base. When your AI assistant asks about a component, it gets the real specification — not hallucinated ARIA attributes. The review_code tool runs 10+ static checks for common anti-patterns (click handlers on divs, missing labels, broken heading hierarchy, positive tabindex, etc.) and cross-references relevant patterns.

No external API calls. No database. Everything runs locally.

Tech Stack

• MCP SDK (FastMCP)
• Python 3.11+
• WAI-ARIA Authoring Practices knowledge base (bundled markdown files)

Related tools

Part of a broader accessibility engineering toolkit. Pair this with:

• screen-reader-cli — CLI for screen-reader-driven testing. Where a11y-expert-mcp gives your AI assistant static guidance (patterns, code review), screen-reader-cli runs live screen-reader checks against real pages using Virtual Screen Reader + Playwright. Static + runtime = full coverage.
• a11y-skills — Canonical source for the pattern instruction files this server serves.
• a11y-engineering-toolkit — Umbrella repo with browser-side audit panel + UX widget, plus the full portfolio map.

License

MIT

Author

Elli (@Elizabeth1979)