Accessibility Testing Skill

WCAG compliance and accessibility quality assurance for iOS applications

Overview

This skill teaches accessibility-first testing strategies for iOS apps. Accessibility testing ensures apps are usable by everyone, including people with disabilities. It combines automated validation of accessibility metadata with manual verification of user experience patterns.

Why accessibility testing matters:

• Legal compliance: WCAG 2.1 is required in many jurisdictions
• User reach: 15% of population has some form of disability
• Better UX: Accessible apps are better for everyone
• SEO benefits: Better structure improves discoverability
• Cost savings: Fix issues early vs. retrofitting

When to Use This Skill

Use this skill when:

1. Validating accessibility compliance before release
2. Debugging VoiceOver issues or user reports
3. Implementing new features that need accessibility support
4. Running accessibility audits as part of CI/CD
5. Testing Dynamic Type support and contrast ratios
6. Verifying semantic markup and element roles
7. Checking keyboard navigation and focus management

This skill covers:

• Accessibility tree analysis and interpretation
• WCAG 2.1 compliance checking (A, AA, AAA levels)
• VoiceOver testing patterns
• Dynamic Type validation
• Common accessibility violations and fixes

Quick Reference

Task	Tool/Operation	Typical Time
Check accessibility quality	accessibility-quality-check	~80ms
Query full accessibility tree	idb-ui-describe	~120ms
Find element by label	idb-ui-find-element	~100ms
Screenshot (fallback only)	screenshot	~2000ms
VoiceOver simulation	Manual testing	-

Core Principle: Accessibility Tree First

The accessibility tree IS your primary testing interface.

Unlike visual testing (screenshots), the accessibility tree reveals:

• What screen readers "see"
• Semantic structure and relationships
• Focus order and navigation paths
• Element roles and states
• Text alternatives for non-text content

3-4x faster and more reliable than visual inspection.

Key Concepts

WCAG 2.1 Levels

Level A (Minimum):

• Text alternatives for images
• Keyboard accessibility
• No color-only information
• Headings and labels present

Level AA (Recommended):

• Contrast ratio 4.5:1 for normal text
• Contrast ratio 3:1 for large text
• Resize text up to 200%
• Meaningful focus order
• Descriptive labels and instructions

Level AAA (Enhanced):

• Contrast ratio 7:1 for normal text
• Contrast ratio 4.5:1 for large text
• No timing requirements
• Comprehensive error handling

Target Level AA for most apps.

iOS Accessibility Properties

Essential Properties:

1. accessibilityLabel: What element is

   • Example: "Profile photo", "Send message button"
   • Should be concise, descriptive

2. accessibilityValue: Current state/value

   • Example: "50%", "Selected", "3 of 10"

3. accessibilityHint: What happens when activated

   • Example: "Opens your profile settings"
   • Use sparingly, only when action isn't obvious

4. accessibilityTraits: Element behavior

   • Button, Link, Header, Selected, etc.

5. isAccessibilityElement: Should be exposed

   • true for interactive/informative elements
   • false for decorative elements

Accessibility Tree vs Visual UI

Accessibility tree is semantic, not visual:

Visual UI:
┌─────────────────┐
│ [img] John Doe  │  ← Visual: Image + Text
│ Online          │
└─────────────────┘

Accessibility Tree:
• Button: "John Doe, Online, Profile"  ← Single focusable element
  - label: "John Doe"
  - value: "Online"
  - hint: "Opens profile"
  - traits: [Button]

Good accessibility = logical semantic structure.

Standard Workflow

1. Initial Accessibility Quality Check

Start here to assess app's accessibility implementation:

{
  "operation": "check-accessibility",
  "target": "booted"
}

Interprets accessibility tree quality:

• "excellent": 90%+ elements have labels, good semantic structure
• "good": 70-90% coverage, minor issues
• "fair": 50-70% coverage, needs improvement
• "poor": <50% coverage, serious accessibility problems
• "insufficient": Cannot perform accessibility-based testing

Decision tree:

excellent/good → Proceed with accessibility-first testing
fair           → Test but expect to find issues
poor           → Major remediation needed
insufficient   → App may not support assistive tech

Note: Most modern iOS apps score "good" or "excellent".

2. Query Accessibility Tree

Core operation for all accessibility testing:

{
  "operation": "describe",
  "target": "booted",
  "parameters": {
    "operation": "all"
  }
}

Returns complete accessibility tree:

{
  "elements": [
    {
      "label": "Login",
      "type": "Button",
      "frame": { "x": 100, "y": 400, "width": 175, "height": 50 },
      "enabled": true,
      "visible": true,
      "traits": ["Button"],
      "value": null,
      "hint": "Sign in to your account"
    },
    {
      "label": "Email address",
      "type": "TextField",
      "value": "",
      "frame": { "x": 50, "y": 300, "width": 275, "height": 44 },
      "enabled": true,
      "visible": true,
      "traits": ["TextField"]
    }
  ]
}

Analyze for:

• All interactive elements have labels
• Labels are descriptive and concise
• Proper element types/traits
• Logical reading order (top-to-bottom, left-to-right)
• No duplicate or confusing labels

3. Validate Specific Elements

Find and verify accessibility of specific UI elements:

{
  "operation": "find-element",
  "target": "booted",
  "parameters": {
    "query": "Submit button"
  }
}

Validates:

• Element exists in accessibility tree
• Has appropriate label
• Correct type and traits
• Enabled/visible state correct

4. Test Navigation and Focus

Verify logical focus order:

1. Query accessibility tree
2. Check elements appear in logical order
3. No gaps in navigation
4. Focus lands on meaningful elements first

Focus order issues:

Bad:  [Button: Cancel] → [Image: Decorative] → [Button: Submit] → [TextField]
Good: [TextField] → [Button: Submit] → [Button: Cancel]

WCAG Compliance Workflows

Testing Checklist

1. Text Alternatives (WCAG 1.1)

All non-text content needs text alternative:

Query accessibility tree for all images
For each image:
  ✓ Has accessibilityLabel
  ✓ Label describes image content
  ✓ Or marked as decorative (isAccessibilityElement: false)

Common violations:

• Images with no label
• Generic labels: "image", "icon", "photo"
• Labels don't describe content: "png_12345"

Fix:

// Bad
imageView.isAccessibilityElement = true // No label

// Good
imageView.isAccessibilityElement = true
imageView.accessibilityLabel = "Profile photo of John Doe"

// Decorative (best if truly decorative)
imageView.isAccessibilityElement = false

2. Keyboard/Focus Navigation (WCAG 2.1)

All functionality available via sequential navigation:

Query accessibility tree
Verify elements appear in logical order:
  ✓ Top to bottom
  ✓ Left to right
  ✓ Grouped logically
  ✓ Interactive elements are focusable
  ✓ Decorative elements are not focusable

Test pattern:

1. describe → Get all elements
2. Map order: element[0], element[1], element[2]...
3. Verify order matches visual/logical flow
4. Check no important elements missing

3. Contrast Ratios (WCAG 1.4.3)

Minimum contrast requirements:

• Normal text (<18pt): 4.5:1 ratio (AA), 7:1 ratio (AAA)
• Large text (≥18pt or ≥14pt bold): 3:1 ratio (AA), 4.5:1 (AAA)
• UI components: 3:1 ratio (AA)

Testing approach:

1. screenshot → Capture current screen
2. Use color picker to sample text/background
3. Calculate contrast ratio: (L1 + 0.05) / (L2 + 0.05)
4. Verify meets WCAG AA (4.5:1 or 3:1)

Common violations:

• Gray text on white: 2.5:1 (fails)
• Light blue on white: 2.8:1 (fails)
• Dark gray on white: 4.6:1 (passes AA)

Note: Screenshots are appropriate for contrast testing (color-based).

4. Labels and Instructions (WCAG 3.3.2)

All inputs have clear labels:

Query accessibility tree
For each TextField/input element:
  ✓ Has accessibilityLabel
  ✓ Label describes purpose
  ✓ Label visible or programmatically associated
  ✓ Required fields indicated
  ✓ Format instructions provided if needed

Good labels:

{
  "type": "TextField",
  "label": "Email address",
  "hint": "Enter your email to sign in",
  "value": ""
}

Bad labels:

{
  "type": "TextField",
  "label": "TextField",  // Generic
  "value": ""
}

5. Dynamic Type Support (iOS-specific)

Text scales from 100% to 200%:

Test pattern:

1. Set Dynamic Type to smallest size
2. Launch app, screenshot, verify readable
3. Set Dynamic Type to largest size
4. Launch app, screenshot, verify:
   ✓ Text scales appropriately
   ✓ No text truncation
   ✓ Layout adapts
   ✓ Buttons still tappable

Settings locations:

• Settings → Accessibility → Display & Text Size → Larger Text
• Simulator: Accessibility Inspector → Settings

VoiceOver Testing Patterns

Simulating VoiceOver Experience

VoiceOver announces elements in accessibility tree order:

1. describe → Get accessibility tree
2. For each element (in order):
   - Announces: [label] [value] [traits] [hint]
   - Example: "Submit button, button, Sign in to your account"
3. Verify announcements are:
   ✓ Clear and descriptive
   ✓ Not redundant
   ✓ Appropriate detail level

Announcement structure:

"[label], [type], [value], [hint]"

Examples:
"Profile photo, image, image of John Doe"
"Volume, slider, 50%, adjustable"
"Send, button, button, Sends your message"

Common VoiceOver Issues

1. Verbose Announcements

Bad:  "Submit button, button, Click here to submit the form"
Good: "Submit, button"

Fix: Remove redundant "button" from label, concise hint.

2. Missing Context

Bad:  "Edit, button" (which item?)
Good: "Edit profile photo, button"

Fix: Include context in label.

3. Confusing Order

Visual:     [Title]  [Close button]
            [Content]
VoiceOver:  Close button → Content → Title  ❌

Fix: Adjust accessibility container order or element grouping.

4. No Label

Element visible, but:
- isAccessibilityElement: false (should be true)
- Or no accessibilityLabel

Fix: Set both properties appropriately.

Common Accessibility Violations

Issue: Image Without Label

Detection:

Query accessibility tree
Find elements with type: "Image"
Check if label is missing or generic

Symptoms:

• VoiceOver says "image" or nothing
• Screen reader users can't identify image

Fix:

imageView.isAccessibilityElement = true
imageView.accessibilityLabel = "Descriptive text"
// Or if decorative:
imageView.isAccessibilityElement = false

Issue: Buttons Without Labels

Detection:

Query accessibility tree
Find elements with traits: ["Button"]
Check if label is missing or just "button"

Symptoms:

• VoiceOver says "button" with no context
• Users don't know what button does

Fix:

button.accessibilityLabel = "Send message"
// Avoid: button.accessibilityLabel = "Send message button" // Redundant

Issue: Low Contrast Text

Detection:

Screenshot → Sample colors
Calculate contrast ratio
Compare to WCAG standards

Symptoms:

• Hard to read in bright light
• Fails WCAG AA (4.5:1)

Fix:

// Increase contrast
label.textColor = .label // System adapts to dark mode
// Or explicit colors with sufficient contrast
label.textColor = UIColor(white: 0.2, alpha: 1.0) // Dark gray on white

Issue: Complex Gestures Required

Detection:

Check if functionality requires:
- Multi-finger gestures
- Precise timing
- Specific swipe patterns

Symptoms:

• Motor-impaired users can't activate
• VoiceOver users can't navigate

Fix:

// Provide alternative single-tap interaction
// Or use standard UIControl components
// Avoid custom gesture-only interfaces

Issue: Non-Descriptive Link Text

Detection:

Query accessibility tree
Find elements with traits: ["Link"]
Check if label is generic: "click here", "read more"

Symptoms:

• Screen reader users don't know destination
• Can't scan links effectively

Fix:

// Bad
link.accessibilityLabel = "Click here"

// Good
link.accessibilityLabel = "Read our privacy policy"

Advanced Testing Patterns

Pattern: Form Validation

Test accessibility of error states:

1. describe → Get form elements
2. Submit invalid form
3. describe → Check error state
4. Verify:
   ✓ Error messages have labels
   ✓ Associated with relevant field
   ✓ Clear instructions for fixing
   ✓ Focus moves to first error

Good error accessibility:

{
  "type": "TextField",
  "label": "Email address",
  "value": "invalid",
  "traits": ["TextField"],
  "hint": "Invalid email format. Example: user@example.com"
}

Pattern: Dynamic Content

Test when content updates:

1. describe → Get initial state
2. Trigger update (load more, filter, etc.)
3. describe → Get new state
4. Verify:
   ✓ New content has labels
   ✓ Loading states announced
   ✓ Focus managed appropriately
   ✓ No duplicate announcements

Use accessibility notifications:

// Announce completion
UIAccessibility.post(notification: .announcement,
                     argument: "10 new messages loaded")

// Or move focus to new content
UIAccessibility.post(notification: .layoutChanged,
                     argument: firstNewElement)

Pattern: Modal/Dialog Testing

Test focus management:

1. describe → Get main screen elements
2. Open modal
3. describe → Get modal elements
4. Verify:
   ✓ Focus trapped in modal
   ✓ Background content not accessible
   ✓ Close button clearly labeled
   ✓ Modal has accessible title
5. Close modal
6. describe → Verify focus returns appropriately

Pattern: Pagination/Lists

Test large scrollable content:

For each page/section:
1. describe → Get visible elements
2. Verify logical reading order
3. Check:
   ✓ Item count announced ("Item 1 of 10")
   ✓ Headings mark sections
   ✓ Load more/pagination clear

Good pagination labels:

cell.accessibilityLabel = "Message from John, Item 5 of 42"
loadMoreButton.accessibilityLabel = "Load 20 more messages"

Automated Testing Integration

CI/CD Accessibility Checks

Basic audit in test pipeline:

1. Launch app to key screen
2. accessibility-quality-check → Get score
3. Assert score >= "good"
4. describe → Capture accessibility tree
5. Validate:
   - All buttons have labels
   - No images without labels (excluding decorative)
   - No duplicate labels in same context
   - Logical element order

Fail build if:

• Score is "poor" or "insufficient"
• Critical elements missing labels
• New violations introduced (regression)

Regression Testing

Track accessibility over time:

1. Capture baseline accessibility tree (JSON)
2. On each commit:
   - Capture current tree
   - Compare to baseline
   - Flag new missing labels
   - Flag changed reading order
3. Review and approve changes or fix regressions

Troubleshooting

Problem: Element Not in Accessibility Tree

Symptoms:

• Element visible but describe doesn't show it
• VoiceOver skips element

Solutions:

1. Check isAccessibilityElement = true
2. Verify not hidden: isHidden = false
3. Check not covered by another element
4. Ensure frame is not CGRect.zero
5. Verify accessibilityElementsHidden = false on parents

Problem: Wrong Reading Order

Symptoms:

• Elements announced in illogical order
• Navigation jumps around screen

Solutions:

1. Check view hierarchy (Z-order affects reading order)
2. Use accessibilityElements array to set explicit order:

   containerView.accessibilityElements = [label, field, button]
   

3. Group related elements in accessibility containers

Problem: Insufficient Context

Symptoms:

• Labels too generic: "button", "image", "item"
• Users can't identify purpose

Solutions:

1. Add specific context to label
2. Include state information in value
3. Use hint for non-obvious actions
4. Consider combining multiple elements:

   containerView.isAccessibilityElement = true
   containerView.accessibilityLabel = "Email from John Doe, unread"
   

Best Practices

1. Accessibility-First Development

Design with accessibility from the start:

• Use standard UIKit components (built-in support)
• Plan semantic structure before visual design
• Consider screen reader experience in wireframes
• Test with VoiceOver during development

2. Semantic HTML/Structure

iOS equivalent:

• Use appropriate UITraits (Button, Header, Link, etc.)
• Group related content in accessibility containers
• Use heading traits to mark sections
• Adjust traits to match element behavior

3. Test with Real Users

Automated testing catches technical issues, but:

• Real screen reader users find UX problems
• Motor-impaired users reveal interaction issues
• Test with VoiceOver on actual device
• Observe usage patterns, not just compliance

4. Document Accessibility Decisions

// Intentionally not accessible - purely decorative
backgroundImage.isAccessibilityElement = false

// Combined for better experience - announces as single element
cardView.isAccessibilityElement = true
cardView.accessibilityLabel = "\(title), \(date), \(author)"
titleLabel.isAccessibilityElement = false
dateLabel.isAccessibilityElement = false
authorLabel.isAccessibilityElement = false

5. Maintain Accessibility Tree Quality

Set standards and enforce:

• Minimum quality score: "good"
• All interactive elements have labels
• All images have labels or marked decorative
• Contrast ratios meet AA standards
• Forms have clear labels and error handling

Measure in CI/CD:

Run: accessibility-quality-check
Assert: score >= "good"
Run: describe → Parse accessibility tree
Assert: All buttons have labels
Assert: No generic labels ("button", "image")

Integration with MCP Tools

This Skill works with these MCP tools:

• accessibility-quality-check: Quick assessment (~80ms)
• idb-ui-describe: Full accessibility tree (~120ms)
• idb-ui-find-element: Semantic element search (~100ms)
• screenshot: Visual inspection (contrast, layout) (~2000ms)

Workflow integration:

1. accessibility-quality-check → Assess app quality
2. idb-ui-describe → Get detailed tree
3. Analyze semantic structure
4. screenshot → Verify contrast/visual (if needed)

Related Skills

• ui-automation-workflows: Accessibility-first UI automation
• ios-testing-patterns: Test strategy and CI integration
• simulator-workflows: Device management for testing

Related Resources

• xc://reference/accessibility: Accessibility API reference
• xc://reference/wcag: WCAG 2.1 guidelines mapped to iOS
• xc://workflows/accessibility-first: This workflow pattern
• xc://examples/voiceover-testing: VoiceOver test examples

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Remember: Accessibility tree is ground truth. Build accessible from the start. Test with real users.