AdCP — Creative Specification

AdCP 3.0 Proposal - This specification is under development for AdCP 3.0. Feedback welcome via GitHub Discussions.

Status: Request for Comments Last Updated: March 2026 The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

Abstract

The Creative Protocol defines a standard interface for creative format discovery, manifest validation, creative generation, and preview rendering. This protocol enables AI agents to discover format specifications, build compliant creative assets, and generate previews across advertising platforms.

Protocol overview

The Creative Protocol provides:

Format discovery with full technical specifications
Manifest validation against format requirements
AI-powered creative generation and transformation
Preview rendering for creative verification
Universal macros for cross-platform tracking

Transport requirements

Creative agents MUST support at least one of the following transports:

Transport	Protocol	Description
MCP	Model Context Protocol	Tool-based interaction via JSON-RPC
A2A	Agent-to-Agent	Message-based interaction

Creative agents SHOULD support MCP as the preferred transport. Creative agents MUST declare Creative Protocol support via get_adcp_capabilities:

{
  "$schema": "https://adcontextprotocol.org/schemas/v3/protocol/get-adcp-capabilities-response.json",
  "adcp": { "major_versions": [2] },
  "supported_protocols": ["creative"],
  "creative": {
    "has_creative_library": true,
    "supports_generation": false,
    "supports_transformation": true,
    "supports_compliance": false
  }
}

The creative capabilities tell the buyer which interaction models this agent supports. See Interaction models below.

Core concepts

Creative agents

A creative agent is any agent that implements the Creative Protocol. This includes standalone services (ad servers, creative management platforms, generative tools) and sales agents that declare "creative" in supported_protocols. A creative agent:

Defines and documents formats it owns
Validates manifests against format requirements
Generates previews showing how creatives will render
Optionally generates or transforms creatives from natural language briefs

Sales agents that implement both the Media Buy Protocol and the Creative Protocol serve both roles from a single endpoint. See Creative capabilities on sales agents.

Interaction models

Creative agents serve different roles depending on their capabilities. Buyers use get_adcp_capabilities to determine which interaction model applies:

Model	Description	Capabilities	Examples
Transformation agent	Resizes or adapts existing manifests to new formats	`supports_transformation: true`	Format conversion services
Generative agent	Creates manifests from natural language briefs	`supports_generation: true`	AI creative platforms
Creative ad server	Hosts a creative library, generates ad-serving tags	`has_creative_library: true`	Flashtalking, CM360, Celtra

These models compose — an agent can support multiple. A creative ad server with supports_generation: true and has_creative_library: true can both generate creatives from briefs and retrieve existing ones from its library. The supports_compliance flag is orthogonal — any interaction model can support compliance requirements in briefs. Buyer workflow by model:

Transformation: list_creative_formats → build_creative (with creative_manifest + target_format_id)
Generation: list_creative_formats → build_creative (with message + target_format_id)
Library retrieval: list_creatives → build_creative (with creative_id + target_format_id)

Agents that host a creative library should also implement the accounts protocol so buyers can establish access before querying. Sales agents that already implement accounts for media buys do not need to do anything additional.

Format authority

Each format has exactly one authoritative creative agent, identified by the agent_url in the format ID:

{
  "format_id": {
    "agent_url": "https://creative.adcontextprotocol.org",
    "id": "display_300x250_image"
  }
}

Creative agents MUST only return authoritative format definitions for formats they own. Creative agents MAY reference other creative agents that provide additional formats.

Formats

Formats define how assets are assembled and rendered. A format specifies:

Media family (display, video, audio, dooh)
Required and optional asset types
Technical constraints (dimensions, duration, file size, codecs)
Rendering behavior and interaction expectations

Assets

Assets are the building blocks of creatives. Asset types include:

image: Static images (JPEG, PNG, WebP, GIF)
video: Video files (MP4, WebM, MOV) or VAST tags
audio: Audio files (MP3, M4A) or DAAST tags
text: Headlines, descriptions, CTAs
html: HTML5 creatives or third-party tags
javascript: JavaScript tags
url: Tracking pixels, clickthrough URLs

Manifests

Manifests pair format specifications with actual asset content. A manifest provides:

Format reference (agent_url + id)
Asset values keyed by asset_id from the format
Tracking URLs and macros

Creative agents MUST validate manifests against format requirements before accepting them.

Universal macros

AdCP defines universal macros for cross-platform tracking. Creative agents MUST support these macros in tracking URLs:

{TIMESTAMP}: Unix timestamp
{CACHEBUSTER}: Random cache-busting value
{CLICK_URL}: Click tracking URL
{REDIRECT_URL}: Final destination URL

Sales agents MUST translate universal macros to their ad server’s native syntax.

Creative Status Lifecycle

Schema: enums/creative-status.json Creatives in a library progress through a defined set of states. archived is the only buyer-initiated state change; all others are seller-initiated (processing, review, approval/rejection).

sync_creatives ──▶ processing ──▶ pending_review ──▶ approved
                       │                                │
                       │ (processing failure)            │ (buyer archives)
                       ▼                                ▼
                   rejected ◀── (policy failure) ── pending_review
                       │                            archived
                       │ (buyer fixes + resubmits        │
                       │  via sync_creatives)             │ (buyer unarchives)
                       ▼                                ▼
                   processing                       approved

Rules:

processing → pending_review: automatic when ingestion and transcoding succeed
processing → rejected: automatic when processing fails (corrupt file, unsupported codec, constraint violation)
pending_review → approved: seller approves after content policy review
pending_review → rejected: seller rejects with rejection_reason
approved → archived: buyer-initiated via sync_creatives
archived → approved: buyer-initiated via sync_creatives (unarchive). Sellers MAY require re-review, transitioning to pending_review instead.
rejected → processing: buyer fixes the creative and resubmits via sync_creatives. The creative re-enters the full processing and review pipeline.
approved → pending_review: seller-initiated re-review (e.g., policy change). Sellers SHOULD notify the buyer when a previously approved creative is pulled back for re-review.

Creative agents MUST reject operations that reference a rejected creative for delivery (e.g., assigning it to a package) with error code CREATIVE_REJECTED. Creative agents MUST include status and rejection_reason (when rejected) in list_creatives responses.

Tasks

The Creative Protocol defines the following tasks. See task reference pages for complete request/response schemas and examples.

list_creative_formats

Reference: list_creative_formats task Discover creative formats and their specifications. Requirements:

Creative agents MUST return full format specifications for formats they own
Creative agents MUST include agent_url identifying the authoritative agent for each format
Creative agents MUST include technical constraints (dimensions, duration, file types) in format definitions
Creative agents MAY include references to other creative agents providing additional formats
When filtering by format_ids, creative agents MUST return only the requested formats

build_creative

Reference: build_creative task Transform, generate, or retrieve creative manifests. Supports three modes:

Generation: Create a manifest from a brief or seed assets
Transformation: Adapt an existing manifest to a different format
Library retrieval: Resolve a creative_id from the agent’s library into a manifest with ad-serving assets (HTML/JavaScript/VAST tags)

Requirements:

Creative agents MUST validate input manifests against format requirements
Creative agents MUST return a valid manifest for the target format on success
Creative agents MUST return validation errors if the transformation cannot be completed
Creative agents SHOULD preserve tracking URLs and macros during transformation
Creative agents SHOULD respect quality for generative tasks ("draft" for fast iteration, "production" for final delivery) and MAY ignore it for non-generative transforms
Creative agents SHOULD honor item_limit when present, using the lesser of item_limit and the format’s max_items
Creative agents MAY use AI/LLM processing for generation tasks
When creative_id is provided, creative agents MUST resolve the creative from their library
When macro_values is provided, creative agents SHOULD substitute the specified macros in the output manifest’s assets and leave unresolved macros as {MACRO} placeholders
Creative agents MUST ignore unrecognized macro keys in macro_values — unknown macros are not an error
Creative agents SHOULD assign globally unique creative_id values; when they cannot guarantee uniqueness, concept_id is REQUIRED on build_creative requests to disambiguate
build_creative supports async responses (status: "working" with context_id polling) for generation and transformation tasks that take significant time. Library retrieval is typically synchronous.

preview_creative

Reference: preview_creative task Generate preview renderings of creative manifests. Requirements:

Creative agents MUST validate manifests before generating previews
Creative agents MUST return preview URLs or HTML for valid manifests
Creative agents MUST include expires_at for preview URLs
Creative agents SHOULD support batch preview for multiple creatives
Creative agents MAY support multiple output formats (URL, HTML, image)

list_creatives

Schema: creative/list-creatives-request.json / creative/list-creatives-response.json Reference: list_creatives task Browse and filter creative assets in a creative library. Implemented by any agent that hosts a creative library — ad servers, creative management platforms, and sales agents that manage creatives. Requirements:

Agents MUST return creatives accessible to the authenticated account
Agents MUST include approval status for each creative
Agents SHOULD support filtering by format, status, tags, and date range
Agents SHOULD support filtering by concept_ids and format_ids when the platform organizes creatives into concepts
Agents MAY include dynamic content variable definitions when include_variables=true
Agents MAY include a lightweight delivery snapshot when include_snapshot=true. The snapshot provides lifetime impressions and last-served date for operational use — detailed analytics belong in get_creative_delivery.

Account requirements:

Creative agents that host a library SHOULD implement the accounts protocol (sync_accounts / list_accounts) so buyers can establish access before querying
This is the same accounts protocol used by sales agents — there is no separate version
Sales agents that already implement accounts for media buys do not need to do anything additional

sync_creatives

Schema: creative/sync-creatives-request.json / creative/sync-creatives-response.json Reference: sync_creatives task Upload and synchronize creative assets in a library. Implemented by any agent that hosts a creative library — ad servers, creative management platforms, and sales agents that manage creatives. Requirements:

Agents MUST validate creatives against format specifications
Agents MUST return validation errors for non-compliant creatives
Agents MAY require approval before creatives are available for use
Agents SHOULD support dry_run for validation without applying changes
Agents MUST reject requests that combine delete_missing: true with creative_ids — delete_missing applies to the entire library, not a filtered subset
Agents that also manage media buys SHOULD support the assignments field for bulk creative-to-package mapping
Standalone creative agents that do not manage media buys SHOULD ignore the assignments field

get_creative_delivery

Reference: get_creative_delivery task Retrieve creative delivery data with variant-level metrics. Requirements:

Agents MUST return delivery data for the requested creatives
Agents SHOULD include variant-level breakdowns when available
Sales agents implementing the Creative Protocol SHOULD support this task when their products generate or optimize creative variants

Error handling

Creative agents MUST return errors using the standard AdCP error schema. Common error codes:

FORMAT_NOT_FOUND: Requested format does not exist
VALIDATION_ERROR: Manifest failed format validation
ASSET_MISSING: Required asset not provided in manifest
ASSET_INVALID: Asset does not meet format constraints
GENERATION_FAILED: Creative generation could not be completed

Security considerations

Transport security

All Creative Protocol communications MUST use HTTPS with TLS 1.2 or higher.

Asset security

Creative agents SHOULD validate that asset URLs are accessible
Creative agents SHOULD scan assets for malware and malicious content
Creative agents MUST NOT execute untrusted JavaScript during validation

Preview security

Preview URLs SHOULD be time-limited (indicated by expires_at)
Creative agents SHOULD sandbox HTML previews to prevent script execution
Consumers of output_format: "html" MUST only use trusted creative agents

Conformance

Creative agent conformance

A conformant Creative Protocol agent MUST:

Support at least one specified transport (MCP or A2A)
Implement list_creative_formats for format discovery
Return authoritative format definitions only for formats it owns
Validate manifests against format specifications
Use specified error codes

A conformant Creative Protocol agent SHOULD:

Implement build_creative for creative generation
Implement preview_creative for preview rendering
Support universal macros in tracking URLs
Implement list_creatives when the agent hosts a creative library
Implement sync_creatives when the agent accepts creative uploads
Support creative_id in build_creative when the agent hosts a creative library
Implement the accounts protocol (sync_accounts / list_accounts) when hosting a creative library
Declare supports_generation, supports_transformation, and has_creative_library in get_adcp_capabilities so buyers can determine the correct interaction model

Consumer conformance

A conformant Creative Protocol consumer MUST:

Use the agent_url from format IDs to identify the authoritative creative agent
Validate manifests against format specifications before submission
Handle validation errors appropriately
Track visited URLs when recursively discovering formats to avoid infinite loops

Implementation notes

Response time expectations

Creative agents SHOULD target the following response times:

Operation Type	Target Latency
Format listing (list_creative_formats)	< 1 second
Library query (list_creatives)	< 1 second
Creative sync (sync_creatives)	< 5 seconds
Preview generation (preview_creative)	< 5 seconds
Batch preview (10 creatives)	< 10 seconds
Creative generation (build_creative)	< 60 seconds

Recursive format discovery

Creative agents MAY reference other creative agents in their list_creative_formats response:

{
  "creative_agents": [{
    "agent_url": "https://creative.adcontextprotocol.org",
    "agent_name": "AdCP Reference Creative Agent",
    "capabilities": ["validation", "assembly", "preview"]
  }]
}

Consumers MAY recursively query referenced agents to discover additional formats. Consumers MUST track visited URLs to prevent infinite loops during recursive discovery.

Format-aware validation

Manifest validation MUST be performed in the context of the format specification:

Look up the format definition from the authoritative creative agent
For each asset in the manifest, find the corresponding entry in the format’s assets array
Validate the asset value against the type and constraints defined in the format

The format definition determines what type each asset_id should be. Asset type information is NOT included in the manifest itself.

Standard vs custom formats

Standard formats: Based on IAB specifications, hosted by the reference creative agent (https://creative.adcontextprotocol.org)
Custom formats: Defined by individual publishers or creative platforms for specialized inventory

Both work identically—the agent_url field identifies which agent is authoritative for each format.

Schema reference

Some creative protocol schemas (build_creative, list_creative_formats, preview_creative) have paths under media-buy/ because they were originally released as part of the media-buy protocol. The schema paths are stable identifiers and do not affect which protocol the task belongs to.

Schema	Description
`core/format.json`	Format definition
`core/creative-manifest.json`	Creative manifest
`core/creative-asset.json`	Asset definition
`media-buy/list-creative-formats-request.json`	list_creative_formats request
`media-buy/list-creative-formats-response.json`	list_creative_formats response
`creative/list-creatives-request.json`	list_creatives request
`creative/list-creatives-response.json`	list_creatives response
`creative/sync-creatives-request.json`	sync_creatives request
`creative/sync-creatives-response.json`	sync_creatives response

Documentation

​Abstract

​Protocol overview

​Transport requirements

​Core concepts

​Creative agents

​Interaction models

​Format authority

​Formats

​Assets

​Manifests

​Universal macros

​Creative Status Lifecycle

​Tasks

​list_creative_formats

​build_creative

​preview_creative

​list_creatives

​sync_creatives

​get_creative_delivery

​Error handling

​Security considerations

​Transport security

​Asset security

​Preview security

​Conformance

​Creative agent conformance

​Consumer conformance

​Implementation notes

​Response time expectations

​Recursive format discovery

​Format-aware validation

​Standard vs custom formats

​Schema reference

Abstract

Protocol overview

Transport requirements

Core concepts

Creative agents

Interaction models

Format authority

Formats

Assets

Manifests

Universal macros

Creative Status Lifecycle

Tasks

list_creative_formats

build_creative

preview_creative

list_creatives

sync_creatives

get_creative_delivery

Error handling

Security considerations

Transport security

Asset security

Preview security

Conformance

Creative agent conformance

Consumer conformance

Implementation notes

Response time expectations

Recursive format discovery

Format-aware validation

Standard vs custom formats

Schema reference