Cookie tracking demo
Site B

This page and example-a.glitch.me both include an iframe from tracker-site.glitch.me, which uses a cookie to track your activity.

As you navigate between this site and example-a.glitch.me, the content of the iframe will be updated to show that tracker-site.glitch.me is tracking your activity on sites where it has a presence.

How it works

1. When you navigate to this page, your browser makes a request to tracker-site.glitch.me for the pink iframe included on the page.
2. The first time your browser requests the iframe from the tracker-site.glitch.me web server, it creates a random id to identify your browser. The server also records the date/time and referer URL of the request.
3. In response to the request, the server provides the iframe document, and includes a header: Set-Cookie: id=<id>.
4. When your browser receives the response, it stores the id cookie.
5. The next time you navigate to a page that includes the iframe from tracker-site.glitch.me, the header Cookie: user-id=<id> is included in the request for the iframe (if third-party cookies are not blocked).
6. When the tracker-site.glitch.me web server receives the request, it gets the cookie value, and checks if it already has a record for that id. If so, it adds the details of the current request to the history it has stored. Otherwise it starts a new entry for the id.
7. The iframe content provided in the response is updated, to display the browsing activity that tracker-site.glitch.me has recorded.