MCP Macros

Procedural macros for the Model Context Protocol (MCP) Rust implementation.

Features

This crate provides procedural macros to reduce boilerplate when defining MCP servers:

#[mcp_server] - Define server metadata and collect tools from impl blocks
#[mcp_tool] - Mark a method as an MCP tool
#[param] - Document tool parameters for the LLM

Usage

use mcp::macros::mcp_server;

#[mcp_server(name = "calculator", version = "1.0.0")]
pub struct CalculatorServer;

#[mcp_server]
impl CalculatorServer {
    #[mcp_tool("Add two numbers")]
    pub fn add(
        &self,
        #[param("First number")] a: f64,
        #[param("Second number")] b: f64,
    ) -> f64 {
        a + b
    }
    
    #[mcp_tool("Multiply two numbers")]
    pub fn multiply(
        &self,
        #[param("First factor")] a: f64,
        #[param("Second factor")] b: f64,
    ) -> f64 {
        a * b
    }
}

Parameter Attributes

All tool parameters (except &self) must be marked with #[param(...)]:

// Shorthand - just the description:
#[param("The user's name")]

// Full form - with additional options:
#[param(description = "The user's name", name = "username", required = true)]

Options:

description - Description shown to the LLM (required for good UX)
name - Custom parameter name override (optional, defaults to argument name)
required - Override required/optional inference (optional, defaults based on Option<T>)

Tool Attributes

// Shorthand - just the description:
#[mcp_tool("Add two numbers")]

// Full form - with additional options:
#[mcp_tool(description = "Add two numbers", name = "custom_add", group = "math")]

License