Why we added engagement signals

During an internal investigation of fourteen days of traffic on one site, we traced 77 of 104 visits counted as human to a single crawler. It followed links between the homepage, signup, and login pages, using rotating residential proxy addresses and an ordinary Chrome user agent. This observation is documented in the project's engineering README; it is not a customer result or a measurement of current filtering accuracy.

The tracker now sends an engagement signal after a real input event while the page is visible, or after the page stays visible for fifteen seconds. Visits with this signal are labeled engaged. Identified bots are filtered, and visits with neither kind of evidence stay unverified. The change does not retroactively classify those historical visits or prove that all engaged visits are human. An unverified visit can still be a real reader.