Struct OnToolErrorContext 

#[non_exhaustive]
pub struct OnToolErrorContext {
    pub tool_name: String,
    pub tool_args: Value,
    pub error: String,
    pub metadata: Value,
}

Context passed to HookPoint::OnToolError hooks.

Error contract

A Rust tool signals failure in one of two ways, and only one of them reaches this hook:

• Returning Err(ToolError) is a hard error. The model sees exactly ToolError::to_string() (the human-readable message), and this hook fires. Any structured metadata attached to the ToolError — which is never shown to the model — is surfaced here on metadata so host code can branch on it.
• Returning Ok(ToolOutput) is a soft result: it is delivered to the PostToolCall hook instead, carrying its own result string and metadata.

This makes success and error handling symmetric: both PostToolCallContext and OnToolErrorContext carry structured metadata alongside their model-facing payload.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

tool_name: String

Name of the tool that errored.

tool_args: Value

Arguments the tool received.

error: String

The error message — exactly what the model sees (ToolError::to_string()).

metadata: Value

Structured metadata attached to the originating ToolError, if any.

This is the error-path counterpart to PostToolCallContext::metadata. It is populated from the ToolError’s metadata map and is never sent to the model — it exists purely for hooks, policies, and logging. Defaults to serde_json::Value::Null when the error carried no metadata.

Implementations

impl OnToolErrorContext

pub fn is_not_found(&self) -> bool

Whether the error denotes a registry-lookup miss, i.e. the model asked for a tool that isn’t registered.

This mirrors ToolError::is_not_found: it inspects metadata for the ERROR_KIND_KEY marker set to KIND_NOT_REGISTERED, letting hosts distinguish a routing miss from a genuine handler failure without matching on message strings.

Trait Implementations

impl Clone for OnToolErrorContext

fn clone(&self) -> OnToolErrorContext

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for OnToolErrorContext

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for OnToolErrorContext

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

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for OnToolErrorContext

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

where __S: Serializer,

Serialize this value into the given Serde serializer.