Enum ContentBlock 

pub enum ContentBlock {
    Text {
        text: String,
        annotations: Option<Annotations>,
        meta: Option<HashMap<String, Value>>,
    },
    Image {
        data: String,
        mime_type: String,
        annotations: Option<Annotations>,
        meta: Option<HashMap<String, Value>>,
    },
    Audio {
        data: String,
        mime_type: String,
        annotations: Option<Annotations>,
        meta: Option<HashMap<String, Value>>,
    },
    ResourceLink {
        resource: ResourceReference,
    },
    Resource {
        resource: ResourceContents,
        annotations: Option<Annotations>,
        meta: Option<HashMap<String, Value>>,
    },
    ToolUse {
        id: String,
        name: String,
        input: HashMap<String, Value>,
        meta: Option<HashMap<String, Value>>,
    },
    ToolResult {
        tool_use_id: String,
        content: Vec<ContentBlock>,
        structured_content: Option<Value>,
        is_error: Option<bool>,
        meta: Option<HashMap<String, Value>>,
    },
}

Content block union — text | image | audio | resource_link | resource | tool_use | tool_result.

Variants

Text

Text content

Fields

text: String

annotations: Option<Annotations>

meta: Option<HashMap<String, Value>>

Image

Image content

Fields

data: String

Base64-encoded image data

mime_type: String

MIME type of the image

annotations: Option<Annotations>

meta: Option<HashMap<String, Value>>

Audio

Audio content

Fields

data: String

Base64-encoded audio data

mime_type: String

MIME type of the audio

annotations: Option<Annotations>

meta: Option<HashMap<String, Value>>

ResourceLink

Resource link (ResourceLink from MCP spec).

Schema: ResourceLink extends Resource — exactly ONE annotations? and ONE _meta?, both inherited from Resource. The flattened ResourceReference is the single source of truth for both — do NOT add variant-level annotations/meta fields alongside it, which would emit the same key twice on the wire.

Fields

resource: ResourceReference

Resource

Embedded resource (EmbeddedResource from MCP spec)

Fields

resource: ResourceContents

annotations: Option<Annotations>

meta: Option<HashMap<String, Value>>

ToolUse

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Tool use content block.

Fields

id: String

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Unique identifier for this tool use

name: String

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Name of the tool being called

input: HashMap<String, Value>

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Input arguments for the tool

meta: Option<HashMap<String, Value>>

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

ToolResult

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Tool result content block.

Fields

tool_use_id: String

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

ID of the tool use this result corresponds to

content: Vec<ContentBlock>

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Content returned by the tool

structured_content: Option<Value>

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Structured content matching the tool’s output schema

is_error: Option<bool>

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Whether the tool call resulted in an error

meta: Option<HashMap<String, Value>>

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface. Earliest removal: first release on/after 2027-07-28.

Implementations

impl ContentBlock

pub fn text(text: impl Into<String>) -> ContentBlock

Create text content

pub fn text_with_annotations( text: impl Into<String>, annotations: Annotations, ) -> ContentBlock

Create text content with annotations

pub fn image( data: impl Into<String>, mime_type: impl Into<String>, ) -> ContentBlock

Create image content

pub fn audio( data: impl Into<String>, mime_type: impl Into<String>, ) -> ContentBlock

Create audio content

pub fn resource_link(resource: ResourceReference) -> ContentBlock

Create resource link

pub fn resource(resource: ResourceContents) -> ContentBlock

Create embedded resource

pub fn tool_use( id: impl Into<String>, name: impl Into<String>, input: HashMap<String, Value>, ) -> ContentBlock

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface.

Create tool use content block

pub fn tool_result( tool_use_id: impl Into<String>, content: Vec<ContentBlock>, ) -> ContentBlock

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface.

Create tool result content block

pub fn tool_result_error( tool_use_id: impl Into<String>, content: Vec<ContentBlock>, ) -> ContentBlock

👎Deprecated since 0.4.0:

Deprecated per SEP-2577 (2026-07-28) with the Sampling surface.

Create tool result error content block

pub fn with_annotations(self, annotations: Annotations) -> ContentBlock

Add annotations to any content block that supports them. ToolUse and ToolResult do not have annotations per spec — this is a no-op for those variants.

pub fn with_meta(self, meta: HashMap<String, Value>) -> ContentBlock

Add meta to any content block

Trait Implementations

impl Clone for ContentBlock

fn clone(&self) -> ContentBlock

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ContentBlock

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for ContentBlock

fn deserialize<__D>( __deserializer: __D, ) -> Result<ContentBlock, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for ContentBlock

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.