Accessibility Test Scanner

Overview

Validate web applications against WCAG 2.1/2.2 accessibility standards covering perceivability, operability, understandability, and robustness. Combines automated scanning with axe-core, Pa11y, and Lighthouse accessibility audits alongside manual validation checklists for keyboard navigation, screen reader compatibility, and color contrast.

Prerequisites

Accessibility testing library installed (axe-core, @axe-core/playwright, Pa11y, or Lighthouse CI)
Browser automation tool (Playwright or Puppeteer) for rendering pages
Application running and accessible at a test URL
Target WCAG conformance level defined (A, AA, or AAA -- AA is standard)
Color contrast analyzer (built into axe-core or standalone tool)

Instructions

Configure the accessibility scanner with the target WCAG level:
- Set axe-core rules to WCAG 2.1 AA (or 2.2 AA for latest standard).
- Include rules for ARIA attributes, color contrast, form labels, and heading structure.
- Define pages and components to scan (homepage, forms, modals, navigation).
Run automated accessibility scans on each page:
- Use @axe-core/playwright to scan after page load.
- Run Pa11y for HTML-level validation.
- Execute Lighthouse accessibility audit for a score and detailed findings.
- Scan each major interactive state (modal open, dropdown expanded, error state).
Validate keyboard navigation:
- Verify all interactive elements are reachable via Tab key in logical order.
- Confirm focus indicators are visible on every focusable element.
- Test Escape key closes modals and dropdowns.
- Verify skip-to-content link is present and functional.
- Check that focus is trapped within open modals (no focus escape).
Validate ARIA implementation:
- Check all ARIA roles match the element's purpose (role="button" on clickable divs).
- Verify aria-label or aria-labelledby on elements without visible text.
- Confirm aria-live regions announce dynamic content changes.
- Validate aria-expanded, aria-selected, and aria-checked states toggle correctly.
Check color and visual accessibility:
- Verify text contrast ratio meets WCAG AA (4.5:1 for normal text, 3:1 for large text).
- Ensure information is not conveyed by color alone (use icons, patterns, or text labels).
- Test with simulated color blindness filters (protanopia, deuteranopia, tritanopia).
Validate form accessibility:
- Every input has an associated <label> with matching for/id.
- Error messages are announced via aria-describedby and aria-invalid.
- Required fields are indicated with aria-required="true" and visual indicators.
Generate a compliance report with WCAG success criteria references for each finding.

Output

Accessibility scan results with violations, passes, and incomplete checks
WCAG compliance matrix showing pass/fail per success criterion
Remediation checklist with code fixes for each violation
Keyboard navigation test results
Lighthouse accessibility score and improvement recommendations

Error Handling

Error	Cause	Solution
axe-core reports no violations but page is inaccessible	Automated tools catch ~30-40% of issues; manual testing needed	Supplement automated scans with keyboard and screen reader manual testing
Color contrast violation on dynamic theme	Theme colors computed at runtime not captured by static scan	Run scans with each theme active (light/dark); test with high-contrast mode
False positive on hidden content	Scanner checks elements that are visually hidden but present in DOM	Use `axe.configure({ rules: [{ id: 'rule-id', selector: ':visible' }] })`
ARIA role conflicts	Multiple conflicting ARIA attributes on same element	Remove redundant roles; follow WAI-ARIA authoring practices for the component pattern
Focus order incorrect after dynamic content	DOM insertion order differs from visual order	Use `tabindex` to correct order; restructure DOM to match visual layout

Examples

Playwright + axe-core accessibility test:

import { test, expect } from '@playwright/test';
import AxeBuilder from '@axe-core/playwright';

test('homepage meets WCAG AA', async ({ page }) => {
  await page.goto('/');
  const results = await new AxeBuilder({ page })
    .withTags(['wcag2a', 'wcag2aa', 'wcag21aa'])
    .analyze();
  expect(results.violations).toEqual([]);
});

test('login form is keyboard accessible', async ({ page }) => {
  await page.goto('/login');
  await page.keyboard.press('Tab');
  const focused = await page.evaluate(() => document.activeElement?.getAttribute('data-testid'));
  expect(focused).toBe('email-input');
  await page.keyboard.press('Tab');
  const nextFocused = await page.evaluate(() => document.activeElement?.getAttribute('data-testid'));
  expect(nextFocused).toBe('password-input');
});

Pa11y CI configuration:

{
  "defaults": {
    "standard": "WCAG2AA",
    "timeout": 10000,  # 10000: 10 seconds in ms
    "wait": 1000  # 1000: 1 second in ms
  },
  "urls": [
    "http://localhost:3000/",  # 3000: 3 seconds in ms
    "http://localhost:3000/login",  # 3 seconds in ms
    "http://localhost:3000/dashboard",  # 3 seconds in ms
    { "url": "http://localhost:3000/settings", "actions": ["click element #tab-profile"] }
  ]
}

Resources

WCAG 2.2 guidelines: https://www.w3.org/TR/WCAG22/
axe-core: https://github.com/dequelabs/axe-core
Pa11y: https://pa11y.org/
WAI-ARIA authoring practices: https://www.w3.org/WAI/ARIA/apg/
Lighthouse accessibility: https://developer.chrome.com/docs/lighthouse/accessibility/
WebAIM contrast checker: https://webaim.org/resources/contrastchecker/

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