Enum MessagePart 

#[non_exhaustive]
pub enum MessagePart {
    Text {
        text: String,
    },
    ToolOutput {
        tool_name: ToolName,
        body: String,
        compacted_at: Option<i64>,
    },
    Recall {
        text: String,
    },
    CodeContext {
        text: String,
    },
    Summary {
        text: String,
    },
    CrossSession {
        text: String,
    },
    ToolUse {
        id: String,
        name: String,
        input: Value,
    },
    ToolResult {
        tool_use_id: String,
        content: String,
        is_error: bool,
    },
    Image(Box<ImageData>),
    ThinkingBlock {
        thinking: String,
        signature: String,
    },
    RedactedThinkingBlock {
        data: String,
    },
    Compaction {
        summary: String,
    },
}

A typed content part within a Message.

Messages may contain zero or more parts that represent heterogeneous content: plain text, tool invocations, memory recall fragments, images, and internal protocol blocks (thinking, compaction). Most providers flatten these into a single string before sending; Claude encodes them as structured content blocks.

Ordering invariants

• ToolUse parts must precede their corresponding ToolResult parts.
• ThinkingBlock / RedactedThinkingBlock parts must be preserved verbatim in multi-turn requests so the API can correctly attribute reasoning.
• Compaction parts must be preserved verbatim; the API uses them to prune prior history on subsequent turns (Claude compact-2026-01-12 beta).

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Text

Plain assistant or user text.

Fields

text: String

ToolOutput

Output from a tool execution, optionally compacted.

Fields

tool_name: ToolName

body: String

compacted_at: Option<i64>

Recall

Memory recall fragment injected by the agent’s semantic memory layer.

Fields

text: String

CodeContext

Repository or file code context injected by the code indexing layer.

Fields

text: String

Summary

Compaction summary replacing pruned conversation history.

Fields

text: String

CrossSession

Cross-session memory fragment carried over from a previous conversation.

Fields

text: String

ToolUse

Model-initiated tool invocation. Pairs with a subsequent MessagePart::ToolResult.

Fields

id: String

name: String

input: Value

ToolResult

Tool execution result returned to the model after a MessagePart::ToolUse.

Fields

tool_use_id: String

content: String

is_error: bool

Image(Box<ImageData>)

Inline image payload (vision input).

ThinkingBlock

Claude thinking block — must be preserved verbatim in multi-turn requests.

Fields

thinking: String

signature: String

RedactedThinkingBlock

Claude redacted thinking block — preserved as-is in multi-turn requests.

Fields

data: String

Compaction

Claude server-side compaction block — must be preserved verbatim in multi-turn requests so the API can correctly prune prior history on the next turn.

Fields

summary: String

Implementations

impl MessagePart

pub fn as_plain_text(&self) -> Option<&str>

Return the plain text content if this part is a text-like variant (Text, Recall, CodeContext, Summary, CrossSession), None otherwise.

pub fn as_image(&self) -> Option<&ImageData>

Return the image data if this part is an Image variant, None otherwise.

Trait Implementations

impl Clone for MessagePart

fn clone(&self) -> MessagePart

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for MessagePart

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for MessagePart

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for MessagePart

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

where __S: Serializer,

Serialize this value into the given Serde serializer.