Trait Tool 

pub trait Tool: Send + Sync {
    // Required methods
    fn name(&self) -> &str;
    fn description(&self) -> &str;
    fn schema(&self) -> ToolSchema;
    fn execute(&self, input: Value) -> ToolFuture;

    // Provided method
    fn execute_structured(&self, input: Value) -> ToolResultFuture { ... }
}

A callable tool the LLM can invoke via tool_calls.

Implementations: FunctionTool (simple fns), MCP adapter (future), graph-as-tool (Plan 014), handoff tools (Plan 009).

Example

struct WeatherTool;

impl Tool for WeatherTool {
    fn name(&self) -> &str { "get_weather" }
    fn description(&self) -> &str { "Get current weather for a city" }
    fn schema(&self) -> ToolSchema {
        ToolSchema {
            name: "get_weather".into(),
            description: "Get current weather for a city".into(),
            parameters: serde_json::json!({
                "type": "object",
                "properties": { "city": { "type": "string" } },
                "required": ["city"]
            }),
            strict: false,
        }
    }
    fn execute(&self, input: Value) -> ToolFuture {
        Box::pin(async move {
            Ok(serde_json::json!({ "temp": 72, "unit": "F" }))
        })
    }
}

Required Methods

fn name(&self) -> &str

Tool name — must be unique within a super::ToolRegistry. Sent to the LLM in the tools list.

fn description(&self) -> &str

Human-readable description of what this tool does. The LLM reads this to decide when to call the tool.

fn schema(&self) -> ToolSchema

JSON Schema for this tool’s input parameters. InjectedState and InjectedStore parameters MUST be excluded.

fn execute(&self, input: Value) -> ToolFuture

Execute the tool with the given input. Called by super::ToolNode.

Provided Methods

fn execute_structured(&self, input: Value) -> ToolResultFuture

Execute with structured result metadata.

Default implementation wraps execute() in ToolResult::ok(). Override to add metadata (result count, source, confidence, etc.).

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl Tool for FunctionTool

impl Tool for StructuredFunctionTool