Key takeaways
- Client-side tracking sends data from JavaScript tags in the visitor’s browser; server-side tracking routes it through a server you control first.
- Browser-based tags miss visits blocked by ad and tracker blockers. GWI data reported by Backlinko put ad blocker use at 29.5% of internet users worldwide and 32.5% in the US in 2025.
- Third-party cookies are not the main issue for first-party analytics. Google kept third-party cookies in Chrome and retired most Privacy Sandbox APIs in October 2025, while Safari’s tracking prevention still shortens script-set cookies.
- Server-side tracking does not remove consent obligations; you must still honor visitor choices and privacy laws.
- A hybrid setup, server-side for key events and ad platform conversions and client-side for general behavior, suits most businesses.
For two decades, analytics has relied on JavaScript tags in the browser. That still works for most visits, but blockers, browser protections and consent choices mean some data never arrives, and ad platforms bid on incomplete conversion signals. This Emulent guide explains where client-side data goes missing, how server-side tracking works and when it is worth the effort.
Why is client-side tracking losing data?
Because more tools and settings stop browser tags from firing or limit what they store.
| Cause of data loss | What happens |
|---|---|
| Ad and tracker blockers | Ad and tracker blockers can block GA4 and ad pixels entirely. Backlinko’s roundup of GWI data estimated 1.77 billion ad-blocking users worldwide in 2025. |
| Safari tracking prevention | Safari’s Intelligent Tracking Prevention caps cookies set by JavaScript, often to seven days and shorter in some link-tracking cases, so returning visitors can look new. |
| Consent opt-outs | Consent opt-outs under GDPR, state privacy laws and similar rules mean some visitors should not be tracked, or only in limited, cookieless form through Google’s consent mode. |
| Privacy browsers and extensions | Privacy browsers and extensions strip tracking parameters and block known analytics domains. |
Chrome’s direction changed: Google decided to keep third-party cookies and wound down most Privacy Sandbox APIs in 2025. That affects ad targeting more than first-party analytics, where blockers and Safari remain the bigger gaps.
How does server-side tracking work?
Data goes from the browser to your own endpoint, then from your server to analytics and ad platforms.
- A lightweight browser tag, or your site’s backend, sends events to a tagging server on a subdomain you control, such as metrics.yourdomain.com.
- A server-side Google Tag Manager container, or a managed service such as Stape, processes events, removes fields you do not want to share and applies consent rules.
- The server forwards events to GA4, the Meta Conversions API, Google Ads enhanced conversions and other destinations.
What it requires:
- Hosting for the container on Google Cloud or a managed provider, with monthly costs that rise with traffic.
- Correct cookie settings, ideally first-party cookies set by your server, which last longer than script-set cookies in Safari.
- Monitoring, updates and documentation, because a broken server container fails silently like any tag.
Should your business switch to server-side tracking?
Usually for some events, not everything.
Consider it when:
- Conversion accuracy drives major spend decisions, especially for paid media bidding on Google and Meta.
- Much of your audience uses Safari or desktop browsers with blockers.
- You need tighter control over what data leaves your site, such as stripping personal details before it reaches vendors.
Client-side alone may be enough when:
- You are a small business without developer support or budget for hosting and maintenance.
- Your main decisions rely on trends rather than exact counts.
For ecommerce, we recommend Shopify, whose built-in Google and Meta channels already send server-side purchase events. For enterprise clients, a hybrid of server-side key events and client-side behavior tracking is the common choice.
How can the Emulent team help?
Emulent evaluates tracking accuracy, recommends client-side, server-side or hybrid setups and implements them with consent controls. A caveat: server-side tracking must still respect consent and privacy laws, and using it to bypass a visitor’s choice creates legal risk; have counsel review your setup in regulated markets. Contact the Emulent team to review your tracking.