Struct CreateMessageParams 

pub struct CreateMessageParams {
    pub messages: Vec<SamplingMessage>,
    pub max_tokens: u32,
    pub system_prompt: Option<String>,
    pub temperature: Option<f64>,
    pub stop_sequences: Vec<String>,
    pub model_preferences: Option<ModelPreferences>,
    pub include_context: Option<IncludeContext>,
    pub metadata: Option<Map<String, Value>>,
    pub tools: Option<Vec<SamplingTool>>,
    pub tool_choice: Option<ToolChoice>,
    pub task: Option<TaskRequestParams>,
    pub meta: Option<Value>,
}

Parameters for a sampling/createMessage request.

Deprecated in MCP 2026-07-28

Sampling is Deprecated by SEP-2577. It remains part of the specification and is still served here, but new implementations should not adopt it, and existing ones should migrate before its earliest removal: the first specification revision released on or after 2027-07-28.

The documented migration path is to integrate with an LLM provider’s API directly rather than asking the client to sample on the server’s behalf.

Nothing is removed from this crate on that date. Removal from the specification does not oblige an SDK to drop a feature, and this crate’s own support follows its release policy, not the specification’s calendar.

Fields

messages: Vec<SamplingMessage>

The messages to send to the LLM

max_tokens: u32

Maximum number of tokens to generate

system_prompt: Option<String>

Optional system prompt

temperature: Option<f64>

Sampling temperature (0.0 to 1.0)

stop_sequences: Vec<String>

Stop sequences

model_preferences: Option<ModelPreferences>

Model preferences

include_context: Option<IncludeContext>

Context inclusion mode

metadata: Option<Map<String, Value>>

Additional metadata

tools: Option<Vec<SamplingTool>>

Tools available for the model to use (SEP-1577)

tool_choice: Option<ToolChoice>

Tool choice mode (SEP-1577)

task: Option<TaskRequestParams>

Legacy 2025-11-25 task parameters for async execution.

This field is invalid on the 2026-07-28 protocol.

meta: Option<Value>

Optional protocol-level metadata

Implementations

impl CreateMessageParams

pub fn new( messages: Vec<SamplingMessage>, max_tokens: u32, ) -> CreateMessageParams

Create a new sampling request

pub fn system_prompt(self, prompt: impl Into<String>) -> CreateMessageParams

Set the system prompt

pub fn temperature(self, temp: f64) -> CreateMessageParams

Set the temperature

pub fn stop_sequence(self, seq: impl Into<String>) -> CreateMessageParams

Add a stop sequence

pub fn model_preferences(self, prefs: ModelPreferences) -> CreateMessageParams

Set model preferences

pub fn include_context(self, mode: IncludeContext) -> CreateMessageParams

Set context inclusion mode

pub fn tools(self, tools: Vec<SamplingTool>) -> CreateMessageParams

Set tools available for the model to use (SEP-1577)

pub fn tool_choice(self, choice: ToolChoice) -> CreateMessageParams

Set tool choice mode (SEP-1577)

Trait Implementations

impl Clone for CreateMessageParams

fn clone(&self) -> CreateMessageParams

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for CreateMessageParams

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for CreateMessageParams

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for CreateMessageParams

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.