ISAPI Programming Examples Internet Server Application Program Interface (ISAPI) is the high-performance server extension API supported by Microsoft Internet Information Server and Peer Web Services. ISAPI allows dynamic responses to HTTP requests, instead of just returning static HTML files. The following links go to two simple ISAPI applications. The first one is for users to do text searches over the HTML pages of the Web site. The second is a favorite sites bulletin board, where users can recommend Web sites to other users who access this Web site.