Documentation Index
Fetch the complete documentation index at: https://docs.adcontextprotocol.org/llms.txt
Use this file to discover all available pages before exploring further.
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.
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
}
}
]
}
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 |
{
"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 |
{
"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
}
}
}
}
| 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
Buyers can filter for accessible formats using the wcag_level parameter in list_creative_formats:
{
"wcag_level": "AA",
"asset_types": ["image", "text"]
}
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
