Content

Content blocks represent displayable information that flows through the Agent Client Protocol. They provide a structured way to handle various types of user-facing content—whether it’s text from language models, images for analysis, or embedded resources for context. Content blocks appear in:

User prompts sent via session/prompt
Language model output streamed through session/update notifications
Progress updates and results from tool calls

Content Types

The Agent Client Protocol uses the same ContentBlock structure as the Model Context Protocol (MCP). This design choice enables Agents to seamlessly forward content from MCP tool outputs without transformation.

Text Content

Plain text messages form the foundation of most interactions.

{
  "type": "text",
  "text": "What's the weather like today?"
}

All Agents MUST support text content blocks when included in prompts.

string

required

The text content to display

Annotations

Optional metadata about how the content should be used or displayed. Learn more.

Image Content

Images can be included for visual context or analysis.

{
  "type": "image",
  "mimeType": "image/png",
  "data": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAAB..."
}

Requires the image prompt capability when included in prompts.

string

required

Base64-encoded image data

string

required

The MIME type of the image (e.g., “image/png”, “image/jpeg”)

string

Optional URI reference for the image source

Annotations

Optional metadata about how the content should be used or displayed. Learn more.

Audio Content

Audio data for transcription or analysis.

{
  "type": "audio",
  "mimeType": "audio/wav",
  "data": "UklGRiQAAABXQVZFZm10IBAAAAABAAEAQB8AAAB..."
}

Requires the audio prompt capability when included in prompts.

string

required

Base64-encoded audio data

string

required

The MIME type of the audio (e.g., “audio/wav”, “audio/mp3”)

Annotations

Optional metadata about how the content should be used or displayed. Learn more.

Embedded Resource

Complete resource contents embedded directly in the message.

{
  "type": "resource",
  "resource": {
    "uri": "file:///home/user/script.py",
    "mimeType": "text/x-python",
    "text": "def hello():\n    print('Hello, world!')"
  }
}

This is the preferred way to include context in prompts, such as when using @-mentions to reference files or other resources. By embedding the content directly in the request, Clients can include context from sources that the Agent may not have direct access to. Requires the embeddedContext prompt capability when included in prompts.

EmbeddedResourceResource

required

The embedded resource contents, which can be either:

Show Text Resource

string

required

The URI identifying the resource

string

required

The text content of the resource

string

Optional MIME type of the text content

Show Blob Resource

string

required

The URI identifying the resource

string

required

Base64-encoded binary data

string

Optional MIME type of the blob

Annotations

Optional metadata about how the content should be used or displayed. Learn more.

Resource Link

References to resources that the Agent can access.

{
  "type": "resource_link",
  "uri": "file:///home/user/document.pdf",
  "name": "document.pdf",
  "mimeType": "application/pdf",
  "size": 1024000
}

string

required

The URI of the resource

string

required

A human-readable name for the resource

string

The MIME type of the resource

string

Optional display title for the resource

string

Optional description of the resource contents

integer

Optional size of the resource in bytes

Annotations

Optional metadata about how the content should be used or displayed. Learn more.

Get Started

Protocol

Libraries

Content Types

Text Content

Image Content

Audio Content

Embedded Resource

Resource Link

​Content Types

​Text Content

​Image Content

​Audio Content

​Embedded Resource

​Resource Link

Content Types

Text Content

Image Content

Audio Content

Embedded Resource

Resource Link