Natural language dialog is an important and intuitive way for people to access information and services. However, current dialog systems are limited in scope, brittle to the richness of natural language, and expensive to produce. This paper introduces Guardian, a crowd-powered framework that wraps existing Web APIs into immediately usable spoken dialog systems. Guardian takes as input the Web API and desired task, and the crowd determines the parameters necessary to complete it, how to ask for them, and interprets the responses from the API. The system is structured so that, over time, it can learn to take over for the crowd. This hybrid systems approach will help make dialog systems both more general and more robust going forward.