accessibility-mcp

A Model Context Protocol server (built with FastMCP) that exposes WAI-ARIA Authoring Practices Guide (APG) patterns: narrative requirements, keyboard/ARIA guidance as Markdown, official example source (HTML, CSS, JS) from w3c/aria-practices, and optional RAG via Ollama + LangChain.js (apg_semantic_search after npm run rag:index).

This is APG (widget patterns), not the full WCAG spec. For WCAG success criteria text, use W3C’s WCAG materials separately; APG is the right source for patterns like Carousel and the patterns index.

Dataset

• npm run ingest — shallow-clones w3c/aria-practices into .cache/, writes:
  • data/manifest.json — compact index (ids, titles, example slugs, bundle paths)
  • data/patterns/<id>.md — pattern doc as Markdown (from *-pattern.html)
  • data/bundles/<id>/<example>.json — referenced HTML/CSS/JS per demo (binary assets listed but omitted)
• npm run rag:index — (after ingest + .env) calls Ollama embeddings and writes data/rag/chunks.json: chunked pattern docs plus one combined text blob per example (HTML/CSS/JS). Re-run after ingest or when you change OLLAMA_EMBEDDING_MODEL.
• Vendored data/ is intended to be committed (or published in the npm package) so the server works without a network. The RAG file can be large; commit or regenerate per machine.

Usage

npm install
npm run ingest   # refresh from GitHub (re-run when you want newer APG)
npm run rag:index # build embeddings (needs Ollama + OLLAMA_EMBEDDING_MODEL)
npm run build
npm start        # stdio MCP server

npx (after publish to npm)

npx -y accessibility-mcp

After the package is on npm, most clients can use command + args with npx / -y / accessibility-mcp instead of a local node path.

Environment (.env)

At startup the server loads .env from the package root (same folder as package.json). Copy .env.example → .env and adjust.

Variable	Purpose
OLLAMA_BASE_URL	Ollama HTTP API root, e.g. http://192.168.1.69:11434 (no trailing slash).
OLLAMA_CHAT_MODEL	Model id for LangChain.js ChatOllama (@langchain/ollama).
OLLAMA_EMBEDDING_MODEL	Model id for OllamaEmbeddings (RAG / similarity).
OLLAMA_SKIP_PULL	If 1 / true / yes, skips /api/pull on startup (models must already exist on the server).
APG_MCP_DATA_DIR	Optional. Directory that contains manifest.json (defaults to data/ next to dist/).

On npm start, the CLI calls Ollama GET /api/tags then POST /api/pull (streaming) for any configured chat/embedding model that is not already present. Progress lines go to stderr only so stdout stays valid for MCP stdio.

Ollama + LangChain.js helpers (for RAG scripts or future MCP tools):

• loadEnv() — load .env explicitly (also runs via getOllamaConfig() / resolveDataDir()).
• getOllamaConfig() — parsed { baseUrl, chatModel, embeddingModel }.
• ensureOllamaModels() — GET /api/tags + POST /api/pull for missing models (same as MCP startup).
• createChatOllama() / createOllamaEmbeddings() — @langchain/ollama instances using those settings.

import { createChatOllama, createOllamaEmbeddings } from "accessibility-mcp";

The apg_semantic_search tool calls Ollama at query time (embed query → cosine similarity vs data/rag/chunks.json). npm run rag:index builds that index with createOllamaEmbeddings().

Sanity check (requires Ollama reachable at OLLAMA_BASE_URL with OLLAMA_CHAT_MODEL pulled):

cp .env.example .env   # then edit if needed
npm run ollama:smoke

---

IDE and agent setup

MCP wiring differs by product: some use a top-level mcpServers object; VS Code uses servers inside mcp.json. Below, replace /absolute/path/to/accessibility-mcp with your clone (or use npx once published).

Shared snippets

Stdio via local build (mcpServers shape — Cursor, Claude Desktop, Claude Code, Gemini CLI):

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

Stdio via npx (after npm publish):

{
  "mcpServers": {
    "apg-patterns": {
      "command": "npx",
      "args": ["-y", "accessibility-mcp"]
    }
  }
}

Custom data directory (any client that supports env on the server process):

{
  "mcpServers": {
    "apg-patterns": {
      "command": "node",
      "args": ["/absolute/path/to/accessibility-mcp/dist/cli.js"],
      "env": {
        "APG_MCP_DATA_DIR": "/absolute/path/to/accessibility-mcp/data"
      }
    }
  }
}

Visual Studio Code (GitHub Copilot agent / MCP)

VS Code stores MCP config in mcp.json using a servers object (not mcpServers). See Add and manage MCP servers in VS Code and the MCP configuration reference.

• Workspace: .vscode/mcp.json
• User: Command Palette → MCP: Open User Configuration

Example (local checkout):

{
  "servers": {
    "apg-patterns": {
      "type": "stdio",
      "command": "node",
      "args": ["/absolute/path/to/accessibility-mcp/dist/cli.js"]
    }
  }
}

Example (npx, after publish):

{
  "servers": {
    "apg-patterns": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "accessibility-mcp"]
    }
  }
}

You can also use MCP: Add Server in the Command Palette or install from the Extensions view (@mcp gallery) if this server is listed there.

Cursor

Cursor merges MCP config from:

• Project: .cursor/mcp.json
• Global: ~/.cursor/mcp.json (project entries override global)

Use the mcpServers JSON shape from the shared snippets above. See Model Context Protocol (MCP) | Cursor Docs. Restart Cursor after changes if tools do not appear.

Claude Desktop

Edit the Claude desktop config file and merge under mcpServers:

OS	Typical path
macOS	~/Library/Application Support/Claude/claude_desktop_config.json
Windows	%APPDATA%\Claude\claude_desktop_config.json
Linux	~/.config/Claude/claude_desktop_config.json

Use the shared mcpServers snippet. Restart Claude Desktop after saving.

Claude Code

Claude Code supports project .mcp.json, user ~/.claude/settings.json, and other scopes; stdio servers use the same mcpServers structure. See Connect Claude Code to tools via MCP and Claude Code settings.

CLI (stdio server):

claude mcp add apg-patterns -- node /absolute/path/to/accessibility-mcp/dist/cli.js

(or with npx after publish: claude mcp add apg-patterns -- npx -y accessibility-mcp)

Gemini CLI

Configure mcpServers in Gemini CLI settings. User vs project scope:

• User: ~/.gemini/settings.json
• Project: .gemini/settings.json in the repo

Details: MCP servers with the Gemini CLI.

CLI (stdio; user scope — writes ~/.gemini/settings.json):

gemini mcp add --scope user apg-patterns node /absolute/path/to/accessibility-mcp/dist/cli.js

Use --scope project to write .gemini/settings.json instead. Run gemini mcp add --help for flags (-e for env, --trust, etc.).

OpenAI Codex (CLI and IDE extension)

Codex stores MCP servers in config.toml, default ~/.codex/config.toml, or project .codex/config.toml on trusted projects. CLI and IDE share this file. See Model Context Protocol – Codex.

TOML example (stdio):

[mcp_servers.apg-patterns]
command = "node"
args = ["/absolute/path/to/accessibility-mcp/dist/cli.js"]

CLI:

codex mcp add apg-patterns -- node /absolute/path/to/accessibility-mcp/dist/cli.js

Other editors

• Windsurf / JetBrains / etc.: If the product documents MCP stdio support, reuse the same command / args as above; the wrapper key name may differ—check that product’s MCP docs.
• VS Code discovery: With chat.mcp.discovery.enabled, VS Code can pick up MCP definitions from some other apps (e.g. Claude Desktop). See the VS Code MCP article.

Tools

Tool	Purpose
apg_meta	Source commit, generation time, patterns index URL
apg_list_patterns	All pattern ids/titles; optional query filter
apg_get_pattern	Markdown spec + example list (patternId, optional includeMarkdown)
apg_get_example	Example sources (patternId, exampleSlug, format: json | markdown)
apg_semantic_search	RAG: natural-language search (query, optional k, maxCharsPerHit); needs npm run rag:index

Resources

• apg://manifest — full manifest JSON
• apg://pattern/{patternId} — pattern Markdown
• apg://example/{patternId}/{slug} — example sources as Markdown

License

ISC (this package). APG content is W3C documentation; see W3C document license.