JsonSchema

The JsonSchema derive macro generates JSON Schema for your struct fields, used by mcp_tool, mcp_resource, and mcp_elicit.

#[derive(macros::JsonSchema)]
pub struct MyTool {
    pub name: String,
    #[json_schema(title = "Age", minimum = 0, maximum = 150)]
    pub age: u32,
    #[json_schema(title = "Tags", max_length = 10)]
    pub tags: Vec<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub optional_field: Option<String>,
}

Supported Attributes

Attribute	Type	Description
title	string	Human-readable field name
description	string	Field description
minimum / maximum	number	Numeric range
min_length / max_length	integer	String length (minLength/maxLength) or array size (minItems/maxItems) for Vec<T> fields
format	string	Format hint (e.g., "email", "uri", "date-time")
default	any	Default value

Required/repeated #[json_schema(...)] attributes can be stacked on a single field.