Struct Ctx 

pub struct Ctx { /* private fields */ }

Context of the request being handled. Declare a Ctx parameter in a tool to receive it; it is excluded from the tool’s input schema.

Cloning is cheap.

Implementations

impl Ctx

pub fn client_supports_apps(&self) -> bool

Whether the client can render MCP Apps interfaces (it declared the extension with the text/html;profile=mcp-app MIME type). A tool can return a richer text answer when it cannot.

impl Ctx

pub fn principal(&self) -> Option<Arc<Principal>>

The caller authenticated by the HTTP transport’s OAuth layer; None when the server does not require authorization (or over stdio).

impl Ctx

pub fn request_id(&self) -> &RequestId

The JSON-RPC id of the request.

pub fn protocol_version(&self) -> &str

The protocol version the client used for this request.

pub fn client_capabilities(&self) -> &ClientCapabilities

The capabilities the client declared for this request.

pub fn client_info(&self) -> Option<&Implementation>

The client’s self-reported identity. Informational only: never use it for security decisions.

pub fn progress_token(&self) -> Option<&ProgressToken>

The progress token, when the client asked for progress notifications.

pub fn client_supports_extension(&self, id: &str) -> bool

Whether the client declared support for an extension.

pub fn cancellation(&self) -> &CancellationToken

A token cancelled when the client cancels the request (stdio notifications/cancelled, or the HTTP response stream closing). Long-running tools should stop work when it fires.

pub fn is_cancelled(&self) -> bool

Whether the request has been cancelled.

pub fn transport(&self) -> &TransportContext

Values attached by the transport.

pub fn state<T: Send + Sync + 'static>(&self) -> Option<State<T>>

Shared state registered with ServerBuilder::state.

impl Ctx

pub fn input_round(&self) -> u32

The number of input rounds completed before this attempt: 0 on the first call, 1 after the client answered once, and so on.

pub fn input_response<T: DeserializeOwned>( &self, key: &str, ) -> Result<Option<T>, ToolError>

The client’s answer for key, decoded as T, if it sent one in this round or an earlier one.

Errors

Returns an invalid-params error (-32602) if the answer does not decode as T.

pub async fn elicit<T: DeserializeOwned + JsonSchema>( &self, key: &str, message: impl Into<String>, ) -> Result<T, ToolError>

Asks the user for structured input with a form generated from T (a flat struct of strings, numbers, booleans and enums). Declining or cancelling becomes a ToolError::user; use elicit_with_action to handle them.

key identifies the question across rounds and must be unique within the handler. Several questions can be asked in one round by awaiting them together (for example with tokio::join!).

Errors

Fails with an “input required” error when the answer is not available yet (propagate it with ?), -32021 if the client does not support form elicitation, and -32602 if the answer is malformed.

pub async fn elicit_with_action<T: DeserializeOwned + JsonSchema>( &self, key: &str, message: impl Into<String>, ) -> Result<Elicitation<T>, ToolError>

Like elicit, but returns declined and cancelled answers instead of failing.

Errors

See elicit.

pub async fn elicit_with_schema( &self, key: &str, message: impl Into<String>, requested_schema: Value, ) -> Result<Elicitation<Map<String, Value>>, ToolError>

Like elicit_with_action, with a hand-written requestedSchema (for default values, titled enums or multi-select fields, which a derived schema cannot express). The accepted content comes back as JSON, for the handler to validate.

Errors

See elicit.

pub async fn sample( &self, key: &str, params: CreateMessageRequestParams, ) -> Result<CreateMessageResult, ToolError>

👎Deprecated:

Sampling is deprecated as of protocol version 2026-07-28 (SEP-2577).

Asks the client to sample from a language model.

Errors

Fails with an “input required” error when the answer is not available yet (propagate it with ?), -32021 if the client does not support sampling, and -32602 if the answer is malformed.

pub async fn list_roots(&self, key: &str) -> Result<ListRootsResult, ToolError>

👎Deprecated:

Roots are deprecated as of protocol version 2026-07-28 (SEP-2577).

Asks the client for its filesystem roots.

Errors

Fails with an “input required” error when the answer is not available yet (propagate it with ?), -32021 if the client does not support roots, and -32602 if the answer is malformed.

impl Ctx

pub fn progress(&self, progress: f64, total: impl Into<Option<f64>>)

Reports progress to the client (notifications/progress), when it asked for it with a progressToken; otherwise does nothing.

Never blocks: if the client reads slowly, only the latest update is kept, and it arrives before the result. progress must increase from one call to the next (smaller values are ignored); total may be omitted with None.

for (i, file) in files.iter().enumerate() {
    ctx.progress(i as f64, files.len() as f64);
    load(file).await;
}

pub fn progress_message( &self, progress: f64, total: impl Into<Option<f64>>, message: impl AsRef<str>, )

Like progress, with a human-readable message.

pub fn wants_progress(&self) -> bool

Whether the client asked for progress notifications.

pub fn log(&self, level: LoggingLevel, data: impl Serialize)

👎Deprecated:

Logging is deprecated as of protocol version 2026-07-28 (SEP-2577); log to stderr with tracing instead.

Sends a log message to the client (notifications/message), when it asked for messages at this level or above; otherwise does nothing. Never blocks; messages beyond the buffer are dropped.

Do not include secrets or internal details: the client sees data. For the server’s own logs, use tracing (stderr).

Trait Implementations

impl Clone for Ctx

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Ctx

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

Formats the value using the given formatter.