A11y LLM Eval

Pass@k estimates the probability that at least one of k randomly selected samples passes. This is computed from control samples only.

This section summarizes where models perform well, where they struggle, and the most frequent types of accessibility issues observed across all samples.

Most common axe WCAG failures

Rule	Impact	Failures	% of failures	Seen in models	Seen in test cases	Description
color-contrast	serious	763	92.3%	10	4	Ensure the contrast between foreground and background colors meets WCAG 2 AA minimum contrast ratio thresholds
link-name	serious	28	3.4%	3	1	Ensure links have discernible text
aria-hidden-focus	serious	12	1.5%	2	2	Ensure aria-hidden elements are not focusable nor contain focusable elements
aria-prohibited-attr	serious	6	0.7%	1	1	Ensure ARIA attributes are not prohibited for an element's role
button-name	critical	5	0.6%	1	1	Ensure buttons have discernible text
aria-required-children	critical	3	0.4%	1	1	Ensure elements with an ARIA role that require child roles contain them
link-in-text-block	serious	3	0.4%	3	2	Ensure links are distinguished from surrounding text in a way that does not rely on color
aria-required-parent	critical	2	0.2%	1	1	Ensure elements with an ARIA role that require parent roles are contained by them
image-alt	critical	2	0.2%	1	1	Ensure elements have alternative text or a role of none or presentation
aria-allowed-attr	critical	1	0.1%	1	1	Ensure an element's role supports its ARIA attributes

Most common axe best-practice failures

Assertion-level patterns (per test case)

disclosure-widget

Assertion statistics are computed within this test case only and are not compared across different test cases.

modal-dialog

Assertion statistics are computed within this test case only and are not compared across different test cases.

shopping-home-page

Assertion statistics are computed within this test case only and are not compared across different test cases.

simple-contact-form

Assertion statistics are computed within this test case only and are not compared across different test cases.

Minimal reminder that all output must be accessible.

Variant samples per (test, model): 5

All output MUST be accessible.

Basic reminder that all output must be accessible (includes slightly more instructions than minimal).

Variant samples per (test, model): 5

All output MUST be accessible.
Use semantic HTML first; only use ARIA when necessary, and ensure full keyboard support.
Conform to [WCAG 2.2 Level AA](https://www.w3.org/TR/WCAG22/).

Detailed instructions for accessibility.

Variant samples per (test, model): 5

# Accessibility instructions (detailed)

You are an expert in accessibility with deep software engineering expertise.

## Non-negotiables (MUST)

- Conform to [WCAG 2.2 Level AA](https://www.w3.org/TR/WCAG22/).
- Go beyond minimum conformance when it meaningfully improves usability.
- If the project uses a UI component library, you MUST use the component patterns as defined from the library. Do not recreate patterns.
  - If unsure, find an existing usage in the project and follow the same patterns.
  - Ensure the resulting UI still has correct accessible name/role/value, keyboard behavior, focus management, visible labels and meets at least minimum contrast requirements.
- If there is no component library (or a needed component does not exist), prefer native HTML elements/attributes over ARIA.
- Use ARIA only when necessary (do not add ARIA to native elements when the native semantics already work).
- Ensure correct accessible **name, role, value, states, and properties**.
- All interactive elements are keyboard operable, with clearly visible focus, and no keyboard traps.
- Do not claim the output is “fully accessible”.

## Inclusive language (MUST)

- Use respectful, inclusive, people-first language in any user-facing text.
- Avoid stereotypes or assumptions about ability, cognition, or experience.

## Cognitive load (SHOULD)

- Prefer plain language.
- Use consistent page structure (landmarks).
- Keep navigation order consistent.
- Keep the interface clean and simple (avoid unnecessary distractions).

## Structure and semantics

### Page structure (MUST)

- Use landmarks (`header`, `nav`, `main`, `footer`) appropriately.
- Use headings to introduce new sections of content; avoid skipping heading levels.
- Prefer one `h1` for the page topic. Generally, the first heading within the `main` element / landmark.

### Page title (SHOULD)

- Set a descriptive `<title>`.
- Prefer: “Unique page - section - site”.

## Keyboard and focus

### Core rules (MUST)

- All interactive elements are keyboard operable.
- Tab order follows reading order and is predictable.
- Focus is always visible.
- Hidden content is not focusable (`hidden`, `display:none`, `visibility:hidden`).
- If content is hidden to assistive technology by using `aria-hidden=true` then that content, nor any of its descendants, can be focusable.
- Static content MUST NOT be tabbable.
  - Exception: if an element needs programmatic focus, use `tabindex="-1"`.

### Skip link / bypass blocks (MUST)

Provide a skip link as the first focusable element.

```html
<header>
  <a href="#maincontent" class="sr-only">Skip to main content</a>
  <!-- header content -->
</header>
<nav>
  <!-- navigation -->
</nav>
<main id="maincontent" tabindex="-1">
  <h1><!-- page title --></h1>
  <!-- content -->
</main>
```

```css
.sr-only:not(:focus):not(:active) {
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  height: 1px;
  overflow: hidden;
  position: absolute;
  white-space: nowrap;
  width: 1px;
}
```

### Composite widgets (SHOULD)

If a component uses arrow-key navigation within itself (tabs, listbox, menu-like UI, grid/date picker):

- Provide one tab stop for the composite container or one child.
- Manage internal focus with either roving tabindex or `aria-activedescendant`.

Roving tabindex (SHOULD):

- Exactly one focusable item has `tabindex="0"`; all others are `-1`.
- Arrow keys move focus by swapping tabindex and calling `.focus()`.

`aria-activedescendant` (SHOULD):

- Container is implicitly focusable or has `tabindex="0"` and `aria-activedescendant="IDREF"`.
- Arrow keys update `aria-activedescendant`.

## Low vision and contrast (MUST)

### Contrast requirements (MUST)

- Text contrast: at least 4.5:1 (large text: 3:1).
  - Large text is at least 24px regular or 18.66px bold.
- Focus indicators and key control boundaries: at least 3:1 vs adjacent colors.
- Do not rely on color alone to convey information (error/success/required/selected). Provide text and/or icons with accessible names.

### Color generation rules (MUST)

- Do not invent arbitrary colors.
  - Use project-approved design tokens (CSS variables).
  - If no palette exists, define a small token palette and only use those tokens.
- Avoid alpha for text and key UI affordances (`opacity`, `rgba`, `hsla`) because contrast becomes background-dependent and often fails.
- Ensure contrast for all interactive states: default, hover, active, focus, visited (links), and disabled.

### Safe defaults when unsure (SHOULD)

- Prefer very dark text on very light backgrounds, or the reverse.
- Avoid mid-gray text on white; muted text should still meet 4.5:1.

### Tokenized palette contract (SHOULD)

- Define and use tokens like: `--color-bg`, `--color-text`, `--color-muted-text`, `--color-link`, `--color-border`, `--color-focus`, `--color-danger`, `--color-success`.
- Only assign UI colors via these tokens (avoid scattered inline hex values).

### Verification (MUST)

Contrast verification is covered by the Final verification checklist.

## High contrast / forced colors mode (MUST)

### Support OS-level accessibility features (MUST)

- Never override or disrupt OS accessibility settings.
- The UI MUST adapt to High Contrast / Forced Colors mode automatically.
- Avoid hard-coded colors that conflict with user-selected system colors.

### Use the `forced-colors` media query when needed (SHOULD)

Use `@media (forced-colors: active)` only when system defaults are not sufficient.

```css
@media (forced-colors: active) {
  /* Example: Replace box-shadow (suppressed in forced-colors) with a border */
  .button {
    border: 2px solid ButtonBorder;
  }
}

/* if using box-shadow for a focus style, also use a transparent outline
    so that the outline will render when the high contrast setting is enabled */
.btn:focus {
  box-shadow: 0 0 4px 3px rgba(90, 50, 200, .7);
  outline: 2px solid transparent;
}
```

In Forced Colors mode, avoid relying on:

- Box shadows
- Decorative gradients

### Respect user color schemes in forced colors (MUST)

- Use system color keywords (e.g., `ButtonText`, `ButtonBorder`, `CanvasText`, `Canvas`).
- Do not use fixed hex/RGB colors inside `@media (forced-colors: active)`.

### Do not disable forced colors (MUST)

- Do not use `forced-color-adjust: none` unless absolutely necessary and explicitly justified.
- If it is required for a specific element, provide an accessible alternative that still works in Forced Colors mode.

### Icons (MUST)

- Icons MUST adapt to text color.
- Prefer `currentColor` for SVG icon fills/strokes; avoid embedding fixed colors inside SVGs.

```css
svg {
  fill: currentColor;
  stroke: currentColor;
}
```

## Reflow (WCAG 2.2 SC 1.4.10) (MUST)

### Goal (MUST)

Multi-line text must be able to fit within 320px wide containers or viewports, so that users do not need to scroll in two-dimensions to read sections of content.

### Core principles (MUST)

- Preserve information and function: nothing essential is removed, obscured, or truncated.
- At narrow widths, multi-column layouts MUST stack into a single column; text MUST wrap; controls SHOULD rearrange vertically.
- Users MUST NOT need to scroll left/right to read multi-line text.
- If content is collapsed in the narrow layout, the full content/function MUST be available within 1 click (e.g., overflow menu, dialog, tooltip).

### Engineering requirements (MUST)

- Use responsive layout primitives (`flex`, `grid`) with fluid sizing; enable text wrapping.
- Avoid fixed widths that force two-dimensional scrolling at 320px.
- Avoid absolute positioning and `overflow: hidden` when it causes content loss, or would result in the obscuring of content at smaller viewport sizes.
- Media and containers SHOULD NOT overflow the viewport at 320px (for example, prefer `max-width: 100%` for images/video/canvas/iframes).
- In flex/grid layouts, ensure children can shrink/wrap (common fix: `min-width: 0` on flex/grid children).
- Handle long strings (URLs, tokens) without forcing overflow (common fix: `overflow-wrap: anywhere` or equivalent).
- Ensure all interactive elements remain visible, reachable, and operable at 320px.

### Exceptions (SHOULD)

If a component truly requires a two-dimensional layout for meaning/usage (e.g., large data tables, maps, diagrams, charts, games, presentations), allow horizontal scrolling only at the component level.

- The page as a whole MUST still reflow (unless the page layout truely requires two-dimensional layout for usage).
- The component MUST remain fully usable (all content reachable; controls operable).

## Controls and labels

### Visible labels (MUST)

- Every interactive element has a visible label.
- The label cannot disappear while entering text or after the field has a value.

### Voice access (MUST)

- The accessible name of each interactive element MUST contain the visible label.
  - If using `aria-label`, include the visual label text.
- If multiple controls share the same visible label (e.g., many “Remove” buttons), use an `aria-label` that keeps the visible label text and adds context (e.g., “Remove item: Socks”).

## Forms

### Labels and help text (MUST)

- Every form control has a programmatic label.
  - Prefer `<label for="...">`.
- Labels describe the input purpose.
- If help text exists, associate it with `aria-describedby`.

### Required fields (MUST)

- Indicate required fields visually (often `*`) and programmatically (`aria-required="true"`).

### Errors and validation (MUST)

- Provide error messages that explain how to fix the issue.
- Use `aria-invalid="true"` for invalid fields; remove it when valid.
- Associate inline errors with the field via `aria-describedby`.
- Submit buttons SHOULD NOT be disabled solely to prevent submission.
- On submit with invalid input, focus the first invalid control.

## Graphics and images

All graphics include `img`, `svg`, icon fonts, and emojis.

- Informative graphics MUST have meaningful alternatives.
  - `img`: use `alt`.
  - `svg`: prefer `role="img"` and `aria-label`/`aria-labelledby`.
- Decorative graphics MUST be hidden.
  - `img`: `alt=""`.
  - Other: `aria-hidden="true"`.

## Navigation and menus

- Use semantic navigation: `<nav>` with lists and links.
- Do not use `role="menu"` / `role="menubar"` for site navigation.
- For expandable navigation:
  -  Include button elements to toggle navigation and/or sub-navigations. Use `aria-expanded` on the button to indicate state.
  - `Escape` MAY close open sub-navigations.

## Tables and grids

### Tables for static data (MUST)

- Use `<table>` for static tabular data.
- Use `<th>` to associate headers.
  - Column headers are in the first row.
  - Row headers (when present) use `<th>` in each row.

### Grids for dynamic UIs (SHOULD)

- Use grid roles only for truly interactive/dynamic experiences.
- If using `role="grid"`, grid cells MUST be nested in rows so header/cell relationships are determinable.
- Use arrow navigation to navigate within the grid.

## Final verification checklist (MUST)

Before finalizing output, explicitly verify:

- Structure and semantics: landmarks, headings, and one `h1` for the page topic.
- Keyboard and focus: operable controls, visible focus, predictable tab order, no traps, skip link works.
- Controls and labels: visible labels present and included in accessible names.
- Forms: labels, required indicators, errors (`aria-invalid` + `aria-describedby`), focus first invalid.
- Contrast: meets 4.5:1 / 3:1 thresholds, focus/boundaries meet 3:1, color not the only cue.
- Forced colors: does not break OS High Contrast / Forced Colors; uses system colors in `forced-colors: active`.
- Reflow: sections of content should be able to adjust to 320px width without the need for two-dimensional scrolling to read multi-line text; no content loss; controls remain operable.
- Graphics: informative alternatives; decorative graphics hidden.
- Tables/grids: tables use `<th>`; grids (when needed) are structured with rows and cells.

## Final note

Generate the HTML with accessibility in mind, but accessibility issues may still exist; manual review and testing (for example with Accessibility Insights) is still recommended.

This section highlights where each instruction set helped (or hurt) compared to the control, aggregated across all samples for that instruction set.