What data do you collect?

Here’s the whole list. It fits on a screen.

About the page: the URL path, the hostname, the page title, and the name of the event if it isn’t a pageview.

About where the visit came from: the referrer, a source and a channel derived from it, and utm_source, utm_medium, utm_campaign, utm_content and utm_term if the link carried them.

About the visitor’s setup: browser and version, operating system and version, device type, screen-size bucket (four buckets, not pixel dimensions), and browser language.

About where they are: country, region and city, looked up from a database on our own disk. The lookup is coarse and there’s no network call - no third party learns anything about your visitor.

About engagement: time on the page and how far down it was scrolled, both accrued only while the tab is visible and focused.

Anything you send us: custom event names, custom properties, and a revenue amount and currency if you’re tracking that.

And one identifier: a 64-bit hash of the user agent, the IP and your domain, keyed to today’s salt. Tomorrow it’s a different number and yesterday’s salt is gone. How that works.

That’s it. Roughly 210 bytes per event on disk. The longer read is what privacy-friendly analytics stores, field by field.

The more interesting list is what we don’t collect - and please don’t put an email address, a user ID or anything else that names a person into a custom property. The DPA forbids it, and there’s no report that would be improved by it.