Aether WCAG Scanner

An MCP server for Claude Code, Cursor, Codex and other coding agents that finds WCAG 2.1 AA accessibility violations and returns ready-to-apply fixes — not just a list of problems.

It drives a real browser (Playwright + axe-core) across desktop, tablet, and mobile viewports, then pairs each violation with a concrete fix: corrected HTML, the relevant WCAG success criteria, and technique code examples.

It works free without a key. For higher quality, contextual fixes, get a beta key at beta.allchemylabs.ai (sign in with GitHub).

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Why it's different

An AI coding agent working from markup alone has to infer what a page does. Aether runs the page in a real browser, measures it with axe-core, and grounds every suggested fix in the WCAG spec, so the agent is working from measurements rather than inference.

	Coding agent alone	Aether, offline	Aether, with API key
How it looks at the page	Reads the HTML it is given	Renders the page in Chromium at desktop, tablet and mobile widths and runs axe-core	Same
What it can measure	Structure visible in the markup	What axe measures on the rendered page: contrast, accessible names, ARIA usage, focusable regions, landmarks	Same
Fix suggestions	From the model's general knowledge	Deterministic templates for the common rules	Templates first, then WCAG-corpus examples, then a model; every cited technique passes a grounding check
How fixes are checked	Not checked unless you set that up	axe re-run on the fixed element; reports what cleared and what regressed	Same
What each fix cites	Whatever the model recalls	The axe rule and its severity	The WCAG success criteria and techniques, with rejected candidates shown
Network	Depends on the agent	None; runs entirely on your machine	Fix requests go to the hosted engine; falls back to offline templates when it is unreachable

Install

/plugin marketplace add https://github.com/allchemylabs/claude-plugins.git
/plugin install aether-wcag-scanner@allchemylabs

Once the official Claude Code marketplace listing is live, you can also install it directly from there.

Installing with /plugin install inside Claude Code prompts for your Allchemy Labs API key; paste the key you got from beta.allchemylabs.ai. Installing from the terminal (claude plugin install …), or letting Claude run the install for you, does not prompt, so set the key afterwards with the command below. Run the same command to change the key later:

/plugin configure aether-wcag-scanner@allchemylabs

The first start installs the plugin's dependencies (about a minute) and the first scan downloads Chromium for Playwright. If /mcp shows the server as not connected right after install, wait a moment and run /reload-plugins.

Running without a key

The plugin asks for a key at install because the cloud fixes need one. The scanner itself runs locally and still works without a key (for example after a terminal install, or via npx): you get local template fixes for every violation. A beta key adds higher quality, contextual fixes from the hosted insights engine; get one at beta.allchemylabs.ai (sign in with GitHub). Set it via the prompt above, or put ALLCHEMY_API_KEY=<key> in the .env of the project you are scanning.

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Use it outside Claude Code (any MCP client)

The same server is published to npm and the MCP Registry as @allchemylabs/aether-wcag-scanner. Any MCP client that speaks stdio can run it:

{
  "mcpServers": {
    "aether-wcag-scanner": {
      "command": "npx",
      "args": ["-y", "@allchemylabs/aether-wcag-scanner"],
      "env": { "ALLCHEMY_API_KEY": "<your beta key>" }
    }
  }
}

The first scan downloads Playwright's Chromium once (about 500 MB on disk: the browser plus its headless shell). Without ALLCHEMY_API_KEY the scanner still runs fully offline and returns template fixes.

Claude Code gets the /wcag-scan skill, which drives the scan → review → fix → verify loop. Other agents only see the tool descriptions and the instructions the server sends at connect time, so for the same behaviour copy AGENTS.md into your project (Codex reads it natively; Cursor and Windsurf accept it as a rules file). Without it an agent may fetch the page HTML and guess instead of running the browser scan.

The 5 tools

Tool	What it does
aether_scan_and_fix	Recommended. Scan a URL — or a single-page app across routes via the spa block — and return violations with fixes, each verified on the real browser, in one call. Set maxFixes: 0 for a fast scan-only pass.
aether_get_fix	Get a fix for one specific violation (verified on the real browser). Omit html to instead get a rule-level explanation — WCAG success criteria and technique examples.
aether_verify_fix	Deterministically verify a fix with real Playwright + axe — re-scan a URL or diff original vs fixed HTML. Reports whether the target cleared, any new regressions, and the net compliance delta.
aether_check_html	Analyze an HTML snippet for issues — no live URL or browser needed.
aether_submit_feedback	Rate a fix (useful / not useful) so the guidance engine keeps improving; your correction helps seed better fixes.

Just ask Claude naturally, e.g. "check localhost:3000 for accessibility issues and fix them" — it will pick the right tool.

The /wcag-scan skill

Run /wcag-scan <url> for a guided workflow: scan → review violations → apply fixes → re-scan to verify → summarize. The skill orchestrates the tools above and edits your files in place.

Hooks

The plugin adds two hooks to Claude Code:

• Session start: checks that the plugin's dependencies and Chromium are installed, and installs them on the first run.
• After each edit: when Claude edits an HTML, JSX, TSX, Vue or Svelte file, a quick heuristic check (no browser) reports possible accessibility issues to Claude. It never blocks an edit, and its findings can be false positives.

To turn the post-edit check off in every project, run /plugin configure aether-wcag-scanner@allchemylabs and set Post-edit accessibility check to false. To turn it off (or back on) for one project, add this to that project's .claude/settings.local.json:

{ "env": { "AETHER_POSTEDIT_HOOK": "0" } }

Use "1" to turn it back on for that project. Restart Claude Code after either change.

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Scanning single-page apps

Pass a spa block to aether_scan_and_fix instead of url:

{ "spa": { "entryUrl": "http://localhost:4200", "framework": "angular", "maxRoutes": 10 } }

• entryUrl — where the app boots. Routes are discovered by crawling client-side links unless you list them in routes: [{ "path": "/settings", "name": "Settings" }].
• framework — angular, react, vue, or omit to auto-detect.
• maxRoutes — cap on discovered routes.

Navigation is client-side (the browser context and app state are kept between routes), and readiness is decided by a layered stability cascade — DOM quiet, framework hooks such as Angular testability, pending-request drain — never by Playwright's networkidle, which deadlocks on apps with long-polling or websockets. A config that sets networkIdle is rejected for that reason.

Requirements

• Node.js >= 20
• Chromium (installed automatically on first run)

Disclaimer

Aether is an accessibility analysis and guidance tool. Using the platform does not, by itself, make your website, application, or digital service conformant with WCAG, the ADA (including Title II), the European Accessibility Act, Section 508, EN 301 549, or any other accessibility law or standard.

Automated scans detect only a subset of accessibility barriers. A "zero issues" result means the scanner did not flag anything in its detection range — not that the property is legally compliant.

You remain responsible for:

• reviewing findings with qualified people
• fixing issues in the underlying code and content
• conducting or commissioning manual testing and audits as needed
• maintaining accessibility as the product changes
• obtaining legal advice for your specific obligations

Aether does not provide legal advice and does not replace an accessibility audit or a VPAT/ACR prepared by a qualified auditor.

License

MIT for the client (this plugin). The hosted insights engine and related Allchemy Labs services are proprietary — see LICENSE and NOTICE.