Derive Macro JsonSchema 

#[derive(JsonSchema)]
{
    // Attributes available to this derive:
    #[json_schema]
}

Derives JSON Schema for a type.

Used for generating input schemas for tools. Generates a json_schema() method that returns the JSON Schema representation of the type.

Example

use fastmcp_rust::JsonSchema;

#[derive(JsonSchema)]
struct MyToolInput {
    /// The name of the person
    name: String,
    /// Optional age
    age: Option<u32>,
    /// List of tags
    tags: Vec<String>,
}

// Generated schema:
// {
//   "type": "object",
//   "properties": {
//     "name": { "type": "string", "description": "The name of the person" },
//     "age": { "type": "integer", "description": "Optional age" },
//     "tags": { "type": "array", "items": { "type": "string" }, "description": "List of tags" }
//   },
//   "required": ["name", "tags"]
// }

Supported Types

• String, &str → "string"
• i8..i128, u8..u128, isize, usize → "integer"
• f32, f64 → "number"
• bool → "boolean"
• Option<T> → schema for T, field not required
• Vec<T> → "array" with items schema
• HashMap<String, T> → "object" with additionalProperties
• Other types → "object" (custom types should derive JsonSchema)

Attributes

• #[json_schema(rename = "...")] - Rename the field in the schema
• #[json_schema(skip)] - Skip this field
• #[json_schema(flatten)] - Flatten nested object properties