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

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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.

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Format Accessibility

Formats declare their accessibility posture through the accessibility object:

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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.

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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).

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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.

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Inspectable Assets

These assets provide structured data that the format uses to render accessibly.
Asset TypeAccessibility FieldsPurpose
Imagealt_textAlternative text for screen readers
Videocaptions_urlURL to captions file (WebVTT, SRT)
transcript_urlURL to text transcript
audio_description_urlURL to audio description track
Audiotranscript_urlURL 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"
    }
  }
}

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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.
FieldTypeDescription
alt_textstringText alternative describing the creative content
keyboard_navigablebooleanCreative can be fully operated via keyboard
motion_controlbooleanRespects prefers-reduced-motion or provides pause/stop controls
screen_reader_testedbooleanCreative 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.

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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 TypeAccessibility Fields
VASTcaptions_url, audio_description_url
DAASTtranscript_url

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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

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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.

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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