Do browsers and ad blockers still block first-party tracking on your own subdomain?

Some do, some do not, and no honest vendor can promise full immunity. Moving tracking to your own subdomain usually helps, but it is not a guarantee, and you can test it yourself in ten minutes.

A story first. A friend runs a small online course business. She moved her tracking script from a third-party address to a subdomain of her own site. Her reported conversions went up. She assumed she had beaten the blockers. Then a customer with a popular blocker installed told her purchases were still missing. Both things were true.

Here is why. Blockers work in more than one way. Some match the domain a request goes to. Some match the file name or the path, like a script called something obvious that appears on lists of known trackers. Some look at what the script does. Moving to your own subdomain defeats the first kind. It may do nothing about the second and third.

Browsers add their own rules. Safari, for example, has protections aimed at cookies set through hidden subdomain aliases, and it limits how long some cookies survive. Brave and some blocker extensions can look behind a subdomain alias to see who is really on the other end. The details change with each release, so please check the current documentation for the browser you care about instead of trusting a blog post, including this one.

What changes with a first-party setup, in general terms: requests go to a name that looks like your own site, so simple domain lists miss them. Cookies are set from your own domain, which browsers tend to treat more kindly than cookies from a stranger. And server-side events do not depend on the browser at all once the data reaches you.

What may still be blocked: a script served with a recognizable name, any request that a blocker decides looks like tracking by behavior, and anything that gets stripped in the browser before it reaches you. Some visitors will always be invisible to browser-side measurement. If a tool tells you otherwise, ask for how they tested it.

Now the part that is useful. Here is a way to test your own site. Open a private window in each browser you care about, once with no extensions and once with a blocker on. Visit the site, click through to a test conversion, and open the developer tools network tab. Look for your tracking requests. Are they sent? Do they come back with a normal response, or are they cancelled by the browser or extension?

Then check cookies. Look at what is stored for your domain and note how long each one lasts. Come back a week later and check again. Some browsers shorten the life of cookies set by scripts, and that is the difference that shows up in returning-visitor reports.

Finally compare counts. Send five test purchases and see how many arrive in your dashboard and how many arrive at the ad platform. A gap tells you more than any claim on a sales page.

A made-up result, to show the shape of it. Ten test visits: four with no blocker, three with a popular blocker, three in a strict browser. Four of four arrive with no blocker. Two of three arrive with the blocker. One of three arrives in the strict browser. That would be a useful, honest picture: better than before, not perfect.

For reference, DataCops runs server-side from your own subdomain and keeps click IDs for up to 90 days. That does not make it unblockable, and you should run the test above on it or any other tool you try.

Who should care most? Sites where a large share of visitors are technical and run blockers, like developer tools, gaming and privacy-minded audiences. For a local plumber, the blocker share may be small enough that this is not your biggest problem.

Have you tested your own site with a blocker on? What did the network tab show?