Enum ToolError 

#[non_exhaustive]
pub enum ToolError {
    InvalidInput(String),
    ExecutionFailed(String),
    Timeout(u64),
    ToolNotFound(String),
    McpError {
        code: i32,
        message: String,
        data: Option<Value>,
    },
    ControlAbort(String),
    PermissionDenied(String),
}

Tool error type.

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.

InvalidInput(String)

Input validation error.

ExecutionFailed(String)

Execution error.

Timeout(u64)

Timeout.

ToolNotFound(String)

Tool not found.

McpError

MCP transport-layer error (adapted via MCPToolAdapter), preserving code/message/data (P1-6).

Not silently downgraded to ExecutionFailed: the caller can distinguish connection drop / method-not-found / argument errors by code.

Fields

code: i32

MCP error code

message: String

MCP error message

data: Option<Value>

Additional error data (optional)

ControlAbort(String)

Framework-level control abort (0.20.0 S3.1).

Distinct from ExecutionFailed: this is the framework refusing to perform the tool call for control-flow reasons (e.g. the handoff cycle / depth guard in lc-agents), not the tool running and failing. Callers must propagate it hard — the agent cannot recover by re-planning, and softening it to an observation would defeat the guard it exists to enforce.

PermissionDenied(String)

Authorization denied (0.22.4 A16): the framework refused to dispatch the tool call before it ran — the target server declares no unattended-execution policy (the MCP fail-closed default), its sandbox rejected the arguments, or its runtime approval gate denied this specific call.

Distinct from ExecutionFailed: the tool never executed, so (unlike ControlAbort) feeding the reason back as an observation lets the agent re-plan or ask for approval.

Trait Implementations

impl Debug for ToolError

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

Formats the value using the given formatter.

impl Display for ToolError

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

Formats the value using the given formatter.

impl Error for ToolError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl From<ToolError> for LcelError

fn from(e: ToolError) -> Self

Converts to this type from the input type.

impl From<ToolError> for CoreError

fn from(source: ToolError) -> Self

Converts to this type from the input type.