A11yScope MCP server

A11yScope

A Chrome extension that checks the current page against the automatable subset of WCAG 2.2 Level AA, and explains each finding in terms a developer can act on.

Built to stay honest about its own limits: automated tooling catches roughly a third of real accessibility barriers, and the UI says so rather than implying a clean scan means compliance.

Two ways to run the same engine:

Both run locally. Nothing is uploaded, no account, no telemetry.

Design constraints

These are not incidental — they shape every decision in the codebase.

server to pay for, and no scan data leaves the browser.

• No backend. Everything runs in the page and the side panel. There is no

Chrome. npm is used only for the test runner.

• No build step. Plain ES modules and classic scripts, loaded directly by

after the user explicitly scans it. This keeps the install-time permission warning minimal, which matters for both review and conversion.

• activeTab, not host permissions. The extension can read a page only

• No runtime dependencies. Nothing in SHIP comes from node_modules.

Layout

manifest.json               MV3 manifest
src/lib/color.js            contrast maths, alpha compositing
src/lib/dom.js              visibility, accessible names, selectors
src/rules/                  the checks, grouped by theme
src/content/engine.js       runs every rule, returns a serialisable report
src/content/highlight.js    injected highlighter (serialised into the page)
src/background/             service worker: tab access and injection
src/panel/                  side panel UI, report export
tools/make_icons.py         draws the PNG icons
tools/package.mjs           builds the Web Store zip from an allow-list
test/                       fixtures and the Chromium-backed test runner

Rules

31 checks across four groups. Each reports either a violation (the failure is unambiguous) or a review item (a real question a human has to answer — never a guess dressed up as a result).

Where a value cannot be determined — text over a background image, a ::placeholder colour, a control hidden off-screen until focused — the rule reports it for review instead of inventing a number. A scanner that cries wolf on correct markup is worse than no scanner.

Some rules only ever ask for review, because the standard itself leaves room for judgement. link-generic-text is the clearest case: WCAG 2.4.4 is Link Purpose In Context, so a "read more" whose meaning comes from the surrounding card conforms. Demanding that link text stand alone is 2.4.9, which is Level AAA.

Calibration

Precision is checked against real sites, not just the fixtures. gov.uk is the control: it is a well-known example of careful accessibility work, so anything we report there is a false positive until proven otherwise.

Shortened. The full README is on GitHub.