Google Tag Gateway Checker

About

See whether any site serves its Google tags (GA4, Ads, GTM, Floodlight) first-party via the Tag Gateway — live as you browse.

Detailed description

Google Tag Gateway Checker tells you — instantly, on every page you open — whether a site
serves its Google tags through a first-party Tag Gateway or lets them fall back to Google's
default domains. No URL to paste, no button to click: it reads the page as you browse and
paints a traffic-light badge on the toolbar.

WHAT IT CHECKS
• Google Analytics 4 (G-)
• Google Ads (AW-)
• Google Tag Manager (GTM-)
• Floodlight / Campaign Manager (DC-)

For each tag it determines how the loader is served:
• First-party — the gtag.js / gtm.js loader comes from the site's own domain (or a sibling
  subdomain). For GA4 it also confirms the /g/collect measurement endpoint is first-party.
• Partial — GA4 only: the loader is first-party but measurement still leaks to
  google-analytics.com (or vice versa). Gateway adoption is incomplete.
• Default — the loader came from www.googletagmanager.com.
• No loader — the tag was seen only in measurement hits, so serving can't be determined.

THE BADGE
A green / amber / red light on the toolbar shows first-party adoption at a glance, with the
number of tags found. Click it for the full breakdown: every tag, its serving state, the
gateway domain, and the underlying requests.

DEEP CHECK (optional)
Some sites hide their gateway behind a custom or obfuscated loader path that ordinary
observation can't attribute. The opt-in "Deep check" button reloads the current page and
follows the request initiator chain — and reads the loader's own script body to match the
GTM runtime signature — so even a renamed first-party loader is recognised by what it does,
not what it's called. Deep check uses Chrome's debugger; Chrome shows its standard
"is debugging this browser" banner while it runs. It's entirely your choice, per page.

PRIVATE BY DESIGN
Everything runs locally in your browser. The extension observes request URLs only — never
response bodies during normal browsing, never page content, never form data. Nothing is sent
to any server, there is no account, and there is no history: live state is held in memory and
cleared when you close the browser. Pause it anytime, or mute specific domains.

WHO IT'S FOR
Analytics engineers, ad-ops and martech teams, and anyone validating a server-side / Tag
Gateway migration who wants to confirm first-party serving in seconds, on real pages, without
opening DevTools.