Accessibility

AdCP accessibility support lets formats declare WCAG conformance levels and requires accessible assets like alt text and captions.

AdCP supports accessibility at two levels: formats declare the conformance level of their rendered output, and assets carry the metadata needed to achieve it.

How It Works

Accessibility in advertising creatives depends on who controls the rendering:

• Format-rendered creatives (image + headline + CTA): The format controls the output. It can guarantee contrast ratios, keyboard navigation, and ARIA landmarks — it just needs the right inputs from the creative (alt text for images, captions for video, etc.).

• Opaque creatives (HTML bundles, JavaScript tags): The format can’t inspect or modify the content. The asset must self-declare its accessibility properties.

AdCP handles both cases through the format’s accessibility object and per-asset-type accessibility metadata.

Format Accessibility

Formats declare their accessibility posture through the accessibility object:

accessibility.wcag_level

The WCAG conformance level that creatives produced by this format will meet. Values: A, AA, AAA.

For format-rendered creatives, this is a guarantee from the format. For opaque creatives, this reflects the level the format requires assets to self-certify to.

accessibility.requires_accessible_assets

When true, all assets with accessibility-relevant fields must include those fields. This is the enforcement mechanism — it tells validation to treat optional accessibility fields as required.

{
  "format_id": {
    "agent_url": "https://creative.adcontextprotocol.org",
    "id": "display_300x250"
  },
  "name": "Display Banner 300x250",
  "accessibility": {
    "wcag_level": "AA",
    "requires_accessible_assets": true
  },
  "assets": [
    {
      "item_type": "individual",
      "asset_id": "hero_image",
      "asset_type": "image",
      "required": true,
      "requirements": {
        "min_width": 300,
        "max_width": 300,
        "min_height": 250,
        "max_height": 250,
        "formats": ["jpg", "png", "webp"]
      }
    },
    {
      "item_type": "individual",
      "asset_id": "headline",
      "asset_type": "text",
      "required": true,
      "requirements": {
        "max_length": 90
      }
    }
  ]
}

This format guarantees WCAG AA output and requires alt_text on the image asset (because alt_text is marked as an accessibility field on the image asset type).

Asset Accessibility Fields

Each asset type defines which of its fields are accessibility-relevant using the x-accessibility schema marker. These fields are always optional by default, but become required when the format sets accessibility.requires_accessible_assets: true.

Inspectable Assets

These assets provide structured data that the format uses to render accessibly.

Asset Type	Accessibility Fields	Purpose
Image	alt_text	Alternative text for screen readers
Video	captions_url	URL to captions file (WebVTT, SRT)
	transcript_url	URL to text transcript
	audio_description_url	URL to audio description track
Audio	transcript_url	URL to text transcript

Example — video asset in a manifest for an accessible format:

{
  "creative_id": "brand_video_001",
  "format_id": {
    "agent_url": "https://creative.adcontextprotocol.org",
    "id": "video_30s_hosted"
  },
  "assets": {
    "video_file": {
      "url": "https://cdn.example.com/video.mp4",
      "width": 1920,
      "height": 1080,
      "duration_ms": 30000,
      "captions_url": "https://cdn.example.com/video.vtt",
      "transcript_url": "https://cdn.example.com/video-transcript.txt",
      "audio_description_url": "https://cdn.example.com/video-ad.mp3"
    }
  }
}

Opaque Assets

HTML and JavaScript assets are black boxes — the format can’t inspect their rendering. These assets carry an accessibility object with self-declared properties.

Field	Type	Description
alt_text	string	Text alternative describing the creative content
keyboard_navigable	boolean	Creative can be fully operated via keyboard
motion_control	boolean	Respects prefers-reduced-motion or provides pause/stop controls
screen_reader_tested	boolean	Creative has been tested with screen readers

Example — HTML creative with accessibility declarations:

{
  "creative_id": "rich_media_001",
  "format_id": {
    "agent_url": "https://publisher.com",
    "id": "rich_media_expandable"
  },
  "assets": {
    "creative_html": {
      "content": "<div class='ad-container'>...</div>",
      "version": "HTML5",
      "accessibility": {
        "alt_text": "Interactive product carousel showing summer collection",
        "keyboard_navigable": true,
        "motion_control": true,
        "screen_reader_tested": true
      }
    }
  }
}

Self-declared accessibility is a trust claim. Platforms may independently validate these properties — that is outside the scope of the protocol.

Third-Party Tags

VAST and DAAST assets wrap video and audio delivered by third parties. They carry accessibility fields alongside their existing tag properties.

Asset Type	Accessibility Fields
VAST	captions_url, audio_description_url
DAAST	transcript_url

Assets Without Accessibility Fields

Some asset types don’t produce standalone rendered content and have no accessibility fields. When a format sets accessibility.requires_accessible_assets: true, these are effectively no-ops:

• Text — rendered by the format
• Markdown — rendered by the format
• CSS — styles, not content
• URL — links, not rendered content
• Webhook — server-side

Discovering Accessible Formats

Buyers can filter for accessible formats using the wcag_level parameter in list_creative_formats:

{
  "wcag_level": "AA",
  "asset_types": ["image", "text"]
}

This returns formats that meet at least WCAG AA conformance and accept image and text assets. The filter uses “at least” logic: requesting AA returns formats with AA or AAA.

Implementation Notes

Enforcement is application-level. The x-accessibility marker is a JSON Schema extension keyword. Standard JSON Schema validators ignore it — enforcement of accessibility.requires_accessible_assets must be implemented in application code that scans asset schemas for x-accessibility: true fields and validates their presence.

For format implementers:

• Set accessibility.wcag_level only when you can substantiate the claim — through your own rendering guarantees or by requiring accessible assets
• If your format renders from structured inputs, ensure your rendering pipeline meets the declared WCAG level (contrast, keyboard nav, ARIA)
• If your format wraps opaque assets, accessibility.requires_accessible_assets: true ensures the inputs carry the right declarations

For creative producers:

• When submitting to a format with accessibility.requires_accessible_assets: true, include all accessibility fields for your asset types
• For opaque assets, test accessibility properties before declaring them
• Provide captions and transcripts as separate hosted files, not embedded in the asset

Related Documentation

• Creative Formats — Format structure and requirements
• Asset Types — Asset specifications and payload schemas
• Creative Manifests — Pairing assets with formats
• list_creative_formats — Format discovery with filtering