Ad Blockers and SourceTag

Ad blockers and privacy extensions can occasionally block SourceTag’s script from loading. This page covers how common the issue is, what happens when the script is blocked, and what you can do about it.

Does SourceTag get blocked?

SourceTag’s script is served from cdn.sourcetag.io. Most ad blockers focus on known advertising and analytics domains like Google Analytics, Facebook Pixel, and major ad networks. SourceTag is not on the major filter lists so the vast majority of ad blockers will not block it.

That said, some aggressive privacy extensions (like uBlock Origin in strict mode or Brave’s built-in shields set to aggressive) may block requests to unfamiliar third-party domains. In those cases, the script would fail to load.

How common is this?

Ad blocker usage varies by audience:

B2B sites typically see 10-20% of visitors using an ad blocker
B2C sites can see 20-30%, sometimes higher for tech-savvy audiences
Most ad blockers use the default filter lists, which do not include SourceTag

In practice, the number of visitors who both have an ad blocker installed and have it configured aggressively enough to block SourceTag is typically very small. For most business websites, the impact is negligible.

What happens when the script is blocked

SourceTag is designed to fail gracefully. If the script doesn’t load:

Forms still work normally. The script not loading has no effect on form submission. Visitors can still fill in and submit forms as usual.
Hidden fields won’t be populated. The attribution data simply won’t be there for that submission. You’ll receive the form data without the st_ fields.
No JavaScript errors. A blocked request doesn’t throw errors or break anything on the page.

The worst case is a missing attribution data point, not a broken user experience.

Workarounds

If ad blockers are blocking SourceTag for a significant portion of your audience, get in touch. We can help set up first-party script serving where the script loads from your own domain instead of cdn.sourcetag.io. Ad blockers almost never block first-party resources.

Tips for maximising coverage

Load the script early. Place the script tag high in the <head> section. The sooner it loads, the less chance of interference from other scripts or extensions.
Use the WordPress plugin or Cloudflare Worker. Both set server-side cookies, which persist even if the JavaScript is blocked on a return visit (the initial visit still needs the script). See WordPress plugin or Cloudflare Worker.
Don’t worry about perfection. No analytics or attribution tool captures 100% of visitors. Even Google Analytics is blocked by ad blockers at a higher rate than SourceTag. The goal is directional accuracy, not absolute completeness.
Monitor your data. If you notice a significant number of form submissions without any SourceTag data, ad blockers might be more prevalent among your audience than expected. The first-party script approach would be the next step.