Struct Tool 

pub struct Tool {
    pub name: String,
    pub title: Option<String>,
    pub description: Option<String>,
    pub output_schema: Option<Value>,
    pub icons: Option<Vec<ToolIcon>>,
    pub annotations: Option<ToolAnnotations>,
    /* private fields */
}

A complete tool definition with service-based execution.

Tools are implemented as Tower services internally, enabling middleware composition via the builder’s .layer() method. The service is wrapped in ToolCatchError to convert any errors (from handlers or middleware) into CallToolResult::error() responses.

Fields

name: String

Tool name (must be 1-128 chars, alphanumeric/underscore/hyphen/dot only)

title: Option<String>

Human-readable title for the tool

description: Option<String>

Description of what the tool does

output_schema: Option<Value>

JSON Schema for the tool’s output (optional)

icons: Option<Vec<ToolIcon>>

Icons for the tool

annotations: Option<ToolAnnotations>

Tool annotations (hints about behavior)

Implementations

impl Tool

pub fn builder(name: impl Into<String>) -> ToolBuilder

Create a new tool builder

pub fn definition(&self) -> ToolDefinition

Get the tool definition for tools/list

pub fn call(&self, args: Value) -> BoxFuture<'static, CallToolResult>

Call the tool without context

Creates a dummy request context. For full context support, use call_with_context.

pub fn call_with_context( &self, ctx: RequestContext, args: Value, ) -> BoxFuture<'static, CallToolResult>

Call the tool with request context

The context provides progress reporting, cancellation support, and access to client requests (for sampling, etc.).

Note

This method returns CallToolResult directly (not Result<CallToolResult>). Any errors from the handler or middleware are converted to CallToolResult::error() with is_error: true.

pub fn with_name_prefix(&self, prefix: &str) -> Self

Create a new tool with a prefixed name.

This creates a copy of the tool with its name prefixed by the given string and a dot separator. For example, if the tool is named “query” and the prefix is “db”, the new tool will be named “db.query”.

This is used internally by McpRouter::nest() to namespace tools.

Example

use tower_mcp::{ToolBuilder, CallToolResult};
use schemars::JsonSchema;
use serde::Deserialize;

#[derive(Debug, Deserialize, JsonSchema)]
struct Input { value: String }

let tool = ToolBuilder::new("query")
    .description("Query the database")
    .handler(|i: Input| async move { Ok(CallToolResult::text(&i.value)) })
    .build()
    .unwrap();

let prefixed = tool.with_name_prefix("db");
assert_eq!(prefixed.name, "db.query");

Trait Implementations

impl Debug for Tool

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

Formats the value using the given formatter.

impl Filterable for Tool

fn name(&self) -> &str

Returns the name of this capability.

impl Send for Tool

impl Sync for Tool