Abstract: A tracking system receives indications of requests for webpages from browsers associated with users' client devices. Upon receiving an indication of a request for a webpage from a client device the tracking system identifies a client ID representing a sharing user associated with the client device. The tracking system hashes the client ID and appends it to the URL of the webpage creating an augmented URL. The browser of the sharing user is redirected to the augmented URL. When a receiving user represented by a different client ID uses the augmented URL to request the webpage, the tracking system determines that the sharing user must have shared the augmented URL with the receiving user and generates a user edge recording the sharing event. The tracking system organizes user edges from sharing events into tree structures and provides visualization functionality to webpage administrators interested in sharing patterns.