Trait ResponseTransformer 

pub trait ResponseTransformer: Send + Sync {
    // Required methods
    fn transform_response(&self, response: Value) -> Value;
    fn transform_schema(&self, schema: Value) -> Value;
}

Transforms tool responses and their corresponding schemas.

Implementors must ensure transform_response and transform_schema are consistent - if a field is removed from responses, it should also be removed from the schema.

Usage

Response transformers can be applied globally to all tools or per-tool:

use std::sync::Arc;
use rmcp_openapi::{Server, ResponseTransformer};

// Global transformer
let mut server = Server::builder()
    .openapi_spec(spec)
    .base_url(url)
    .response_transformer(Arc::new(RemoveNulls))
    .build();

server.load_openapi_spec()?;

// Per-tool override
server.set_tool_transformer("verbose-endpoint", Arc::new(AggressiveFilter))?;

Resolution Order

1. Per-tool transformer (if set) takes precedence
2. Else global server transformer
3. Else no transformation

Required Methods

fn transform_response(&self, response: Value) -> Value

Transform the response body before returning to MCP client.

This method is called after each successful tool call to transform the JSON response body. The transformation should be consistent with transform_schema - any fields removed here should also be removed from the schema.

Arguments

• response - The JSON response body from the HTTP call

Returns

The transformed response body

fn transform_schema(&self, schema: Value) -> Value

Transform the output schema to match response transformations.

This method is called when:

• Loading the OpenAPI spec (for global transformers)
• Setting a per-tool transformer

The schema transformation should reflect what transform_response will do to the actual responses.

Arguments

• schema - The JSON Schema for the tool’s output

Returns

The transformed schema

Implementors