Struct ToolOutcome 

pub struct ToolOutcome {
    pub text: String,
    pub structured: Option<Value>,
    pub is_error: bool,
}

One tool call’s outcome, in MCP’s own shape.

Three states, not two. Result can say “it worked” or “it failed”, but a tool that RAN and declined — a quota refusal, a guard saying no, a provider that needs reconnecting — is neither: the model should read the reason and adapt, exactly as it reads a success. Collapsing that into Err throws away the text the model needed; collapsing it into Ok tells the model it succeeded.

Fields

text: String

Text handed to the model.

structured: Option<Value>

Machine-readable payload mirrored into MCP structuredContent.

is_error: bool

MCP isError. True for a refusal the model should adapt to.

Implementations

impl ToolOutcome

pub fn json(value: Value) -> Self

A successful call carrying JSON. The text is the compact encoding, which is what a model reads when a server sends no separate rendering.

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

A successful call carrying prose.

pub fn refused(reason: impl Into<String>) -> Self

The tool ran and declined. reason is for the model, not the operator.

pub fn with_structured(self, value: Value) -> Self

Attach structured content to a refusal, so a caller can carry a machine -readable code alongside the prose.

Trait Implementations

impl Clone for ToolOutcome

fn clone(&self) -> ToolOutcome

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ToolOutcome

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

Formats the value using the given formatter.