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Version: 1.1.0 (latest)

Logging

The server can send structured log messages to the client using MCP logging notifications.

// Send a structured log message to the client
runtime.notify_log_message(LoggingMessageNotificationParams {
    level: LoggingLevel::Info,
    logger: Some("my-server".into()),
    data: serde_json::json!({
        "event": "user_login",
        "user_id": "abc123",
        "timestamp": "2025-01-01T00:00:00Z",
    }),
    meta: None,
}).await?;

The client controls the minimum logging level via the handle_set_level_request server handler method:

async fn handle_set_level_request(
    &self, params: SetLevelRequestParams, _runtime: Arc<dyn McpServer>,
) -> Result<Result, RpcError> {
    println!("Client set logging level to: {:?}", params.level);
    Ok(Result::default())
}

Add the logging capability to ServerCapabilities in your InitializeResult so clients know you accept logging/setLevel (see Quickstart for the full setup):

capabilities: ServerCapabilities {
    logging: Some(Default::default()),
    ..Default::default()
},