Disclosed embodiments include a distributed system and server for detecting changes to web pages comprises (a) a Web Change Detection (WCD) server connected to the network, and (b) one or more WCD agents stored on the WCD server configured to be executed directly on a web browser to detect web page changes. The WCD comprises (a) an agent storage module configured to store the WCD agents, (b) a WCD repository to store a WCD information regarding the web pages in the server memory, and (c) a WCD changes detector configured for receiving information sent by the WCD agents and detecting changes on the web pages. The WCD system relies on the web users accessing sites to collaboratively detect the changes on the web pages, eliminating the need for crawler estimates of web-page changes.