See how long each Google tag takes to load, client-side and server-side

Time every Google request on the page

Turn on Check Google tags in a Performance Test page config and the run also records every outbound Google tag request: GTM's gtm.js, gtag.js, GA4 collect hits, and Google Ads and DoubleClick requests. Each one shows its own network duration and how long after navigation it fired.

Offsets are a practical guide ("did GTM load in the first second or the eighth?"), not a micro-benchmark.

Client-side and server-side in one toggle

The same toggle covers tags loaded straight from Google's domains and tags proxied through the brand's own domain by server-side GTM or first-party mode. That makes it a direct way to compare the two setups on the same page. GA4 hits are labelled v=2, so an old Universal Analytics request sharing the same path isn't miscounted as GA4.

Beacon hits may show as failed

A GA4 hit sent as a beacon around page unload often shows a failed status here, even when the browser delivered it, the same behaviour described in Read delivery verdicts. For delivery questions, use the Network Requests Inspector; use this timing view for when and how long.

Tests fire real tags

Unlike the form test, the Performance Test doesn't block anything, because blocking would make the timings meaningless. Every run is a real page load with real tags firing and real pageviews sent. The volume is low and easy to filter: add the test machine's IP to GA4's internal-traffic rules if you test production often.

Keep going

• Measure page speed
• Inspect every collect request
• QA for every release