With the rapid growth of the World Wide Web, more and more people rely on the online services to acquire and integrate information. However, it is time consuming to find the online services that are perfectly suited for a given task. First, the users might not have enough information to fill in the required input fields for querying an online service. Second, the online service might generate only partial information. Third, the user might only find the inverse version of the desired service. In this paper we propose a framework to develop flexible web agents that handle these imperfect situations. In this framework we exploit a search engine as a general information discovery tool to assist finding and pruning information. To demonstrate this framework, we implemented two web agents: the Internet inverse geocoder and the address lookup module.