container audit

GTM-TZWXFFZ

This container ships 121 hand-written scripts (40 KB of JavaScript) to every visitor — more than 99% of the 46,522 containers we have measured. That is an application's worth of code, delivered as tag configuration.

Measurement runs through a server container on its own domain — the mark of a mature setup, and rarer than the tooling vendors imply.
459 published versions — each one live for every visitor the moment it was published.

Tags341

Custom scripts121

Third parties23

Delivered854 KB

Versions459

What we observed

A real browser loaded macmillan.org.uk a month ago and recorded every request it made. This is what happened, as distinct from what the container is configured to do. It is one page load — anything that fires only deeper in the site did not fire here.

Container loaded from googletagmanager.com — Google

Measurement sent to capi.macmillan.org.uk — not Google

Measurement is first-party; the container still loads from Google. These are separate decisions, and this is the more common of the two.

Forwarded to GA4 ×8 — read from the measurement id, not the hostname

Consent OneTrust answered its own API. 5 measurement hits left the page before it was granted, carrying a client id (whether that is permitted depends on jurisdiction, and this was not a European visit). no new hosts appeared after granting — either the tags are ungated, or they fire regardless and record the decision. Google recorded gcs=G111 (all granted). 10 advertising hosts were contacted before anything was granted.

Third parties contacted 25 hosts — cdn.cookielaw.org, dev.visualwebsiteoptimizer.com, geolocation.onetrust.com, www.googletagmanager.com, t.contentsquare.net, unpkg.com, cdn.corvidae.ai, c.az.contentsquare.net, and 17 more

dataLayer events seen pageLoad, OneTrustLoaded, OptanonLoaded, gtm.js, gtm.dom, gtm.load, gtm.scrollDepth

Where the data goes

Confirmed — a browser watched this site send measurement data to capi.macmillan.org.uk, not to Google. observed on macmillan.org.uk More info »

Findings

Ordered by consequence. review has a concrete cost when it bites; info is real but depends on your setup. Seen is how common it is across the containers we have measured — reported separately on purpose, because common and harmless are different claims.

reviewHardcoded http:// URL (4)

4 pieces of custom code reference a plain http:// address.

WhyOn an https:// page the browser blocks or upgrades these. Blocked means the tag quietly stops working; upgraded only works if that host also serves https.

CheckCheck whether the hosts below still respond over https, and update the URLs.

Seenseen in 12.8% of 46,522 containers measured

reviewWrites cookies directly (1)

1 piece of custom code set cookies in code.

WhyCookies set this way bypass GTM's consent settings, because the consent checks live in the tag templates rather than in raw JavaScript.

CheckIf any of these cookies are used for analytics or advertising, confirm they are still gated on a consent decision.

Seenseen in 21.2% of 46,522 containers measured

infoLoads JavaScript from another host (26)

26 pieces of custom code fetch and run JavaScript from another host.

WhyWhatever that host serves executes with full access to the page — it can read the DOM, cookies and form fields. The code is not in this container, so it can change at any time without any change here.

CheckConfirm you recognise every host below and that someone owns the relationship. A host you cannot name is the one to chase.

Seenseen in 54.4% of 46,522 containers measured

infoVendor IDs written into custom code (6)

6 vendor IDs are pasted directly into custom HTML rather than held in a variable or template.

WhyChanging a property, pixel or account then means editing every tag that mentions it, and any one that gets missed keeps sending to the old destination indefinitely.

CheckFine if the ID never changes. If you have ever migrated a property, check that none of these still point at the old one.

Seenseen in 31.4% of 46,522 containers measured

infoConsent configuration detected (3)

The container declares one or more consent signals.

WhyConsent handling is present in the container. This describes what the artifact declares; what actually happened on the page is measured separately, above.

CheckConfirm these settings match the consent policy you intend to enforce, and compare them with the before-and-after observation.

Seenseen in 44.6% of 46,522 containers measured

Third parties it can reach

Each host is a party that can execute code or receive data in a visitor's browser. Follow one to see who else loads it. More info »

What the custom templates can do

Custom templates are third-party code shipped inside the container. Injecting scripts and running page globals is ordinary for them — most tag templates need it to work — so this is an inventory, not a warning. It lists the capability each template declares so you can match it against templates you meant to install.

__cvt_MBTSV gallery injects code from stapecdn.com · runs page-level globals

__cvt_KF8K9 gallery injects code from analytics.tiktok.com · runs page-level globals

__cvt_13443930_1090 private injects code from x.dotomi.com, x.macmillan.org.uk

__cvt_13443930_940 private runs page-level globals

__cvt_13443930_1028 private injects code from static.ads-twitter.com · runs page-level globals

__cvt_5RM3Q gallery injects code from connect.facebook.net · runs page-level globals

__cvt_MRQN8 gallery runs page-level globals

Detected on

Sites observed loading this container. A container used across many hosts is a shared template; one on a single host is a bespoke build. Follow a site to see every container it loads.

macmillan.org.uk

What this audit describes

Containers change. These findings describe one specific artifact, and you can re-fetch it to check this reading.

Container	`GTM-TZWXFFZ`
Published version	`459` — the identity of this configuration. It changes only when someone publishes.
Read at	2026-08-23 18:14:40 UTC (a month ago)
Source	`https://www.googletagmanager.com/gtm.js?id=GTM-TZWXFFZ`
Body checksum	`d4b8fd6b6eb407bbfbf03d82d8685601c5c5062a3eba2508ff2453a0f27b1a3f` Evidence of the exact bytes we read, not an identity: Google varies the response per request, so re-fetching an unchanged container yields a different checksum. Compare the published version instead.

Re-audit

This reading is from a month ago. A container can be republished at any time, and nothing here updates on its own — a fresh read is the only way to know whether it still says this. Running it again replaces this page in place, so the link keeps working.

Re-audit GTM-TZWXFFZ

Check another container

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