We recently ran into an interesting issue with one of our clients: their site was rejecting URLs—and the culprit wasn’t immediately obvious.
After digging in, we found the cause: GA4’s cross-domain tracking parameters, specifically, _gl and _ga, and _gcl, were being appended to URLs and triggering the rejection. These parameters are part of Google Analytics 4’s automatic link decoration for cross-domain tracking, but in some cases, they can trip up server configurations, firewalls, or legacy code that doesn’t expect or allow unfamiliar query strings.
If you’ve ever encountered strange redirect issues, broken pages, or unexplained URL rejections, and you're using GA4 cross-domain tracking, keep reading.
What Are _gl and _ga Parameters?
When GA4 cross-domain tracking is enabled, Google appends two query parameters to the destination URL:
_gl– Carries encoded attribution and session data. It’s short for “Global Link” and is used to maintain session continuity across domains._ga– Used for GA4’s Client ID to stitch user sessions between domains.
Example URL:
https://othersite.com/page?_gl=1*xyz&_ga=2.123456.789101112.1
Why This Can Be a Problem
In our client’s case, their code was rejecting these URLs outright—possibly due to:
- A server-side validation rule that doesn’t allow unexpected query parameters.
- Redirects or routers that break when special characters (like
*,.or=) appear in query strings. - A firewall or WAF (Web Application Firewall) that treats unknown query parameters as suspicious.
- Legacy systems that treat clean URLs as a requirement and silently fail when parameters are added.
If your own server, code, or third-party integration isn’t expecting _gl or _ga parameters, this can break your site's behavior, links, or tracking.
What You Can Do About It
- Check Server Rules or Redirect Logic
See if your server or app has rules that filter, rewrite, or reject URLs with query strings. You might need to allowlist these GA4 parameters or update your parsing logic. - Test Links with Parameters
Manually test a link with GA4 parameters added. Does it load? Does the redirect still work? If not, check your server logs or browser console for clues. - Review Your Cross-Domain Configuration
If you don't need cross-domain tracking between two domains, consider disabling it to prevent parameter injection in the first place. - Review Your Conversion Linker Tag for cross domain tracking as well. If you don't need them then remove them.
- Sanitize Parameters Carefully
If you're stripping query parameters for any reason (e.g., for cleaner URLs), make sure you’re not doing it in a way that breaks GA4 tracking or session continuity.
Final Thoughts
GA4 brings a lot of automation to the table—cross-domain tracking being one of them. But if your infrastructure isn’t prepared for the query parameters it uses, you might find yourself debugging strange URL issues.
If something suddenly starts breaking and you're using GA4, don't forget to inspect the URLs and look for _gl and _ga parameters. These small tokens can have a big impact on your user experience, especially if your site is strict about query strings.
Have you run into similar issues? Drop me a note, I'd love to hear how you're handling it.
Related GA4 Posts
- How to Set Up GA4 Cross-Domain Tracking
- Understanding GA4 Session and Engagement Metrics
- Step-by-Step Guide to GA4 eCommerce Tracking
- GA4 vs Universal Analytics: What’s Changed?