keyboard-a11y-tester

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 Basics

  • General

    Note that other projects may use the same name.

    An AI-assisted web accessibility tester that behaves like two W3C personas at once: a keyboard-only user ("Ade") and a screen-reader user ("Lakshmi"). It drives a page keyboard-only, records what happens at every focus stop, and emits evidence-linked findings mapped to specific WCAG success criteria — against any website.

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    keyboard-a11y-tester

    An AI-assisted web accessibility tester that behaves like two W3C personas at once: a
    keyboard-only user ("Ade") and a screen-reader user ("Lakshmi"). It drives a page
    keyboard-only, records what happens at every focus stop, and emits evidence-linked
    findings mapped to specific WCAG success criteria — against any website. Both
    personas run in the same pass by default; a --persona flag restricts to just one.

    It has two layers:

    • a deterministic runner (scripts/runner.mjs) that owns the mechanical, reproducible
      work — driving the page keyboard-only, capturing a per-step trace + screenshots, and
      computing the machine-decidable checks for both personas;
    • an AI-judgment layer — the invoking agent — that reads the trace/screenshots/census
      and judges what rules can't (task completion, logical focus/reading order, form
      quality, announcement quality). See SKILL.md for how an agent drives it.

    Standalone and portable: it depends only on playwright, yaml, pngjs, pixelmatch,
    and @guidepup/virtual-screen-reader, needs no bundled test cases, and writes all output
    to a per-user temp directory (never into this folder). The screen-reader persona
    never drives a real screen reader (NVDA/VoiceOver) — see "Screen-reader detection" below.

    Documentation: docs/usage.md (setup, dependencies, quick start,
    CAPTCHAs) · docs/interface.md (full CLI reference, output file
    schema, WCAG checks table).

    Quick start

    As a Claude Code plugin — register this repo as a plugin marketplace, then install it:

    /plugin marketplace add ezufelt/keyboard-a11y-tester
/plugin install keyboard-a11y-tester@ezufelt

    The first command registers this repo as a marketplace (named ezufelt, per
    .claude-plugin/marketplace.json); the second installs the plugin. Once installed, the
    skill in SKILL.md becomes available to the agent.

    As a standalone clone — clone the repo and install its dependencies:

    git clone https://github.com/ezufelt/keyboard-a11y-tester.git
cd keyboard-a11y-tester
npm install
npx playwright install chromium

    Then drive it directly (see Run against any URL).

    Requirements & dependencies

    Requires Node.js ≥ 20 and Chromium (via Playwright), plus five small npm dependencies —
    no build step. Run node scripts/setup-check.mjs to verify both before your first run.

    See docs/usage.md for the full dependency
    table, licensing credit for @guidepup/virtual-screen-reader, and setup instructions.

    Run against any URL (no test file needed)

    # quick unattended blind Tab-crawl of the start page, per viewport
node scripts/runner.mjs --url https://example.com

# a full scenario, driven live by the agent one keystroke at a time
node scripts/runner.mjs serve --url https://example.com --goal "find the pricing page" \

     --viewport desktop --port 9400
#   → prints:  READY <session-dir>   (under the system temp dir)
node scripts/runner.mjs observe <session-dir>
node scripts/runner.mjs step    <session-dir> --press Tab      # one keystroke; prints observation
node scripts/runner.mjs step    <session-dir> --press Enter
node scripts/runner.mjs step    <session-dir> --type "hello@example.com"
node scripts/runner.mjs finish  <session-dir>                  # writes trace + findings
node scripts/runner.mjs stop    <session-dir>

    See docs/usage.md for the full
    quick-start walkthrough, and docs/interface.md for every CLI flag and
    the complete output file schema.

    Authenticated runs

    Pages behind a login can't be tested with a fresh, logged-out browser. Pass a Playwright
    storageState JSON file with --storage-state <file> to start the browser with its cookies
    and localStorage already loaded (e.g. an already-logged-in session). Generate one with
    context.storageState({ path: 'auth.json' }) or npx playwright codegen --save-storage=auth.json <url>.
    The file is validated (exists, parses as JSON, and looks like a real storageState export —
    i.e. has cookies/origins arrays) before the browser launches — a missing or malformed file
    fails the run immediately rather than silently testing the logged-out site. In serve mode
    it's applied once at launch and the session browser keeps the state alive for every subsequent
    step.

    A storageState file holds live session cookies/tokens — treat it as a secret. Don't commit
    it; .gitignore already excludes auth.json, storageState.json, and *storage-state*.json,
    but a differently-named file won't be caught automatically.

    What the runner does (deterministic layer)

    Playwright (full Chromium, new-headless + SwiftShader for real pixels) drives the page with
    only the keyboard — it never calls .click() or .focus(); if a control is only
    reachable by pointer, that is itself a finding. It drops to a raw CDP session for the
    accessibility tree (Accessibility.getPartialAXTree), the ground truth for name/role/state.
    At startup it fails fast if :focus-visible does not fire on CDP-driven key events
    (every focus-indicator check would otherwise be invalid) — skipped entirely when
    --persona screen-reader is passed, since that persona has no pixel/focus-ring work.

    Checks are evaluated per focus stop the persona actually visits (keyboard persona) or
    against a page-wide structural census (screen-reader persona) — this is scenario
    testing, not an exhaustive page audit. Conformance target: AA is pass/fail, AAA is
    informative.

    WCAG Level Persona Check
    2.4.7 AA keyboard Focus indicator present
    2.4.13 AAA (informative) keyboard Focus indicator strength
    1.4.1 AA keyboard Indicator is not colour-only
    2.1.2 AA keyboard Keyboard trap
    2.4.1 AA keyboard No skip link
    2.4.3 AA keyboard Positive tabindex
    3.2.1 AA keyboard Context change from focus alone
    3.3.2 AA keyboard File input named only by the user-agent default ("Choose File")
    4.1.2 AA keyboard Focusable control with no accessible name
    1.1.1 AA screen-reader Missing alt text/aria-label
    1.3.1 AA screen-reader Heading level skip
    1.3.1 AA screen-reader Duplicate, unlabeled landmark roles
    4.1.2 AA screen-reader Interactive control announced as a bare role
    4.1.3 AA screen-reader Declared live region that never announced anything

    See docs/interface.md for the authoritative version of
    this table (full check descriptions) and the W3C persona references.

    Output

    Everything is written under a per-user temp dir (${TMPDIR}/keyboard-a11y-tester/…, or
    --out): a trace.json (per-step evidence), deterministic-findings.json (WCAG findings),
    screen-reader-census.json (screen-reader persona), and cropped screenshots/step_NNNN.png
    per viewport. See docs/interface.md for the
    complete directory layout and field-by-field schema of every output file.

    Focus-visible detection (2.4.7 AA presence + 2.4.13 AAA strength)

    Presence (AA) uses two independent signals, so a faint-but-real indicator is never
    missed:

    1. the focused element's computed style declares an outline or box-shadow (ground
      truth — recorded in the trace as computed_focus_style), or
    2. pixels change on focus (catches background/colour indicators with no outline).

    Either one means the indicator is present → AA pass. Pixel diffing compares the focused
    frame to a scroll-aligned baseline (the next step's frame, where the element is no longer
    focused — so focus is never manipulated programmatically), measuring ring slices at
    increasing offset (thin and offset outlines), the interior, and top/bottom edge bands.

    Strength (AAA, informative) measures whether the indicator meets 2.4.13 Focus
    Appearance — changed area ≥ a 2px-thick perimeter of the control, and ≥ 3:1 WCAG luminance
    contrast between focused and unfocused states. Advisory only. (This measure is unreliable
    on pages that mutate between steps — e.g. "load more" — because the neighbour-frame
    baseline then differs by content, not just the focus ring; treat AAA numbers on such pages
    with caution. AA presence is unaffected, being driven by the computed style.)

    So 2.4.7 (AA) requires only that an indicator is visible with no size/contrast minimum: a
    faint 1px or low-opacity ring passes AA and is flagged weak at AAA — rather than being
    falsely reported as "no focus indicator."

    Screen-reader detection (Lakshmi)

    The screen-reader persona is emulated, never driven for real: @guidepup/virtual-screen-reader
    builds an ARIA/ACCNAME-spec accessible tree over the live page and computes what a
    spec-compliant screen reader would announce, entirely in the browser's own JS engine — no
    NVDA/JAWS/VoiceOver is launched, and it works the same way on any OS the runner itself
    supports.

    Its self-contained browser bundle is injected via Playwright's context.addInitScript,
    which is not subject to the page's own CSP — verified against both a synthetic CSP-locked
    page and a real CSP-locked production site. Once injected, its virtual cursor tracks
    real keyboard focus automatically     (it listens for native focusin events), so every
    step you drive with real Tab/Enter/etc. produces a matching sr_announcement with no
    separate "chasing" logic and no drift between what's focused and what's reported as
    announced. The same mechanism also wires a MutationObserver that computes WAI-ARIA
    live-region semantics and captures "assertive: …"/"polite: …" announcements as they
    happen — this is what 4.1.3 (Status Messages) findings are derived from.

    Separately, once per newly-visited page URL, an ephemeral instance walks the entire page
    in reading order (never touching the live per-step monitor) to build
    screen-reader-census.json — the source for the heading-hierarchy, duplicate-landmark,
    missing-alt-text, and bare-role-control checks, since those need whole-page context rather
    than just the stops a keyboard user's Tab order happens to visit.

    This augments but does not replace testing with a real screen reader and real users —
    the upstream library's own README says exactly that, and it's worth repeating: this checks
    what a spec-compliant screen reader should announce given the page's ARIA/HTML, not the
    specific quirks of any one real screen reader implementation.

    CAPTCHAs

    CAPTCHAs detect automation and refuse to run; the runner has a page-scoped, human-approved
    compatibility workaround. See docs/usage.md for details.

    License

    MIT © Everett Zufelt. See LICENSE.

 Controls 0/19 ●

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Project badge entry owned by: ezufelt.
Entry created on 2026-07-10 18:22:26 UTC, last updated on 2026-07-10 21:04:01 UTC. Last achieved passing badge on 2026-07-10 21:04:01 UTC.