Struct FunctionTool 

pub struct FunctionTool { /* private fields */ }

A tool created from an async Rust function.

FunctionTool wraps an async closure and exposes it as a Tool that LLM agents can invoke. Use the builder methods to configure schema, execution flags, and required scopes.

Implementations

impl FunctionTool

pub fn new<F, Fut>( name: impl Into<String>, description: impl Into<String>, handler: F, ) -> Self

where F: Fn(Arc<dyn ToolContext>, Value) -> Fut + Send + Sync + 'static, Fut: Future<Output = Result<Value>> + Send + 'static,

Create a new FunctionTool from an async handler function.

pub fn with_long_running(self, long_running: bool) -> Self

Mark this tool as long-running (prevents duplicate invocations).

pub fn with_read_only(self, read_only: bool) -> Self

Mark this tool as read-only (safe for parallel dispatch).

pub fn with_concurrency_safe(self, concurrency_safe: bool) -> Self

Mark this tool as concurrency-safe (can run in parallel with other tools).

pub fn with_parameters_schema<T>(self) -> Self

where T: JsonSchema + Serialize,

Derive the parameters JSON Schema from a type implementing JsonSchema.

pub fn with_response_schema<T>(self) -> Self

where T: JsonSchema + Serialize,

Derive the response JSON Schema from a type implementing JsonSchema.

pub fn with_scopes(self, scopes: &[&'static str]) -> Self

Declare the scopes required to execute this tool.

When set, the framework will enforce that the calling user possesses all listed scopes before dispatching execute().

Example

let tool = FunctionTool::new("transfer", "Transfer funds", handler)
    .with_scopes(&["finance:write", "verified"]);

pub fn parameters_schema(&self) -> Option<&Value>

Get the parameters schema, if set.

pub fn response_schema(&self) -> Option<&Value>

Get the response schema, if set.

Trait Implementations

impl Tool for FunctionTool

fn enhanced_description(&self) -> String

Returns an enhanced description for long-running tools that includes a note warning the model not to call the tool again if it’s already pending.

fn name(&self) -> &str

Returns the unique name of this tool.

fn description(&self) -> &str

Returns a human-readable description of what this tool does.

fn is_long_running(&self) -> bool

Indicates whether the tool is a long-running operation. Long-running tools typically return a task ID immediately and complete the operation asynchronously.

fn is_read_only(&self) -> bool

Indicates whether this tool performs no side effects. Read-only tools may be executed concurrently in Auto mode.

fn is_concurrency_safe(&self) -> bool

Indicates whether this tool is safe for concurrent execution. Used by the Parallel strategy to validate dispatch safety.

fn parameters_schema(&self) -> Option<Value>

Returns the JSON Schema for this tool’s parameters, if any.

fn response_schema(&self) -> Option<Value>

Returns the JSON Schema for this tool’s response, if any.

fn required_scopes(&self) -> &[&str]

Returns the scopes required to execute this tool.

fn execute<'life0, 'async_trait>( &'life0 self, ctx: Arc<dyn ToolContext>, args: Value, ) -> Pin<Box<dyn Future<Output = Result<Value>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Executes the tool with the given context and arguments.

fn declaration(&self) -> Value

Returns the tool declaration that should be exposed to model providers.

fn is_builtin(&self) -> bool

Indicates whether this tool is a built-in server-side tool (e.g., google_search, url_context).