Marc Alexander, Google Tag Manager consultant
Marc audits, rebuilds and documents GTM containers so the data is right, your team can change them safely, and the next site release doesn't break them. He has 10 years in digital analytics, from running all of VisitBritain's tagging through Tag Manager to auditing a 236-tag estate at Halfords.
Results from recent work.
- 236 tagsin the Halfords container, audited line by line, with 30 ranked findings
- Over halfof the tags on Halfords' order confirmation page would count an order again on refresh
- 48 to 12dataLayer pushes in the redesigned MOT booking journey for Halfords' new site
- 0back-end changes at The Super Prime: the full GA4 ecommerce funnel built in Tag Manager, live in under two weeks
The detail is in the case studies for Halfords and The Super Prime.
Signs your container needs attention.
Nobody dares touch it.
An agency or developer built it and left. Tags fire for reasons no one can explain, nothing is documented, and every change feels like a risk.
Every release breaks something.
Triggers tied to CSS classes or page layout fail whenever the site changes. A proper dataLayer and stable identifiers survive redesigns and platform moves.
The platforms disagree.
GA4 says one thing, Google Ads another, Meta a third and the CRM something else. Usually the tags read different values at different moments.
Years of clutter.
Duplicate tags, old triggers and unused variables pile up. They slow the site down and send the same data twice.
Orders counted twice.
Tags on the confirmation page fire again when it's refreshed. At Halfords, over half of the tags on that page would have counted the same order again.
Page views missing on a single-page app.
Standard triggers don't fire when a React or Vue site changes route. These sites need history-change handling and dataLayer events designed for them.
Google tags outside the container.
Hard-coded gtag config calls run alongside Tag Manager and can count the same visit twice. Since October 2026 each one shows in Preview as a gtag.config event.
What a GTM consultant does.
Tag Manager decides what every tracking and advertising tag on your site sends, and when. A GTM consultant, or Tag Manager specialist, makes sure it gets that right. You end up with:
- An audit of every tag, trigger and variable in the container
- A clean-up, or a rebuild with clear naming and documentation
- A dataLayer specification your developers can build against
- GA4, Google Ads, Meta, LinkedIn and TikTok tags reading the same values
- Consent Mode v2 wired in and tested with real clicks
- Ecommerce tracking from product view to purchase, on Shopify, WooCommerce or Magento
- Tracking that survives redesigns, releases and single-page app route changes
Where Tag Manager sits in the flow.
- Your websitePage views, clicks, purchases and forms, written to a dataLayer the site owns.
- ConsentConsent Mode v2 by region: nothing personal leaves until the visitor agrees.
- Google Tag ManagerOne container, every tag documented and checked against consent.
- Server-side taggingWhere it earns its place: one stream to your own subdomain, with control over what each platform gets.
- GA4 and ad platformsGoogle Analytics 4, Google Ads and Meta each get what they're allowed, once.
- BigQuery and reportingRaw data joined to the CRM and finance, and dashboards that match the ledger.
Clean up or rebuild?
The most common question about an untidy container. The audit answers it for yours, but these are the usual signs.
Clean up when…
- Naming and structure are mostly consistent
- Triggers are built on dataLayer events
- Someone on the team understands how it works
- There's a handful of custom scripts, each with a clear job
Rebuild when…
- There's no consistent naming or structure
- Triggers depend on CSS classes and page layout throughout
- Nobody can explain what large parts of it do
- The site is moving to a new platform anyway, as with Halfords' headless migration
A rebuild is typically £1,200 to £3,500. It costs more up front and much less to maintain.
Tag Manager projects.
Container audit
What every tag does, what it sends and what consent it relies on.
- Findings ranked by risk, with container-only fixes separated from development work.
- Custom code checked for defects, as in the register of 20 found at Halfords.
Clean-up or rebuild
Clear naming, no duplicates and nothing firing that nobody can explain. A rebuild is typically £1,200 to £3,500.
- Done in stages, so reporting keeps its continuity.
- Every change tested in Preview mode before it's published.
New build and dataLayer
A container built on events the site provides. A new setup is typically £800 to £2,500.
- A dataLayer specification written as developer user stories.
- The free dataLayer specification template shows the format.
Tracking without developer time
When the site can't change soon, the tracking layer can be built in Tag Manager alone.
- Listings, carousels, property pages and enquiries at The Super Prime, found by page structure, not CSS classes.
- Background form submissions picked up from network requests.
Consent in Tag Manager
Tags that wait for the right consent, checked with real clicks.
- For Hertility Health, a bespoke consent script built from scratch to replace a third-party platform and its licence, keeping Consent Mode v2 and category-based script blocking.
- Region-specific defaults in one container. See consent by region.
Moving to the new tagging experience
Optimising a container for Google's destinations without losing a setting or a conversion.
- Every Google tag's settings recorded first, the ones you don't own left as legacy, then consent and conversions tested in Preview before anything is published.
- See what the new tagging experience changes and the optimisation checklist.
Server-side Tag Manager
A server container on your own subdomain, from £2,000.
- At Halfords, the Meta, TikTok and Reddit conversions API feeds and the customer data platform feed rebuilt on Stape Data Tags, replacing 10 workaround GA4 tags.
- See server-side GTM and Stape.
GTM audit: what's checked.
A Google Tag Manager audit goes through the container line by line. It covers:
- Every tag: what it sends, to which platform, and on which pages
- Triggers and firing order, including tags that depend on each other
- The consent each tag relies on, and whether it really waits for it
- Duplicates and double counting, such as tags that fire again when a confirmation page is refreshed
- Custom HTML and JavaScript, checked for defects and risky code
- Personal data reaching the dataLayer, URLs or tags where it shouldn't
- Unused tags, triggers and variables
- Scripts that slow pages down
- Who can publish, and whether changes have version notes
Findings are ranked by risk, with the cheap container-only fixes separated from work that needs developers. The GA4 mini audit includes a check of the container alongside GA4.
How a project runs.
Review
The current container, what it sends and where, and what the business needs to measure.
Plan
An event scheme, a dataLayer specification for developers, and which platforms get which data.
Build and test
Built in a workspace and tested in Preview mode, on staging, across browsers, with consent granted and refused.
Launch and hand over
Published in stages, checked against live data, documented, with a walkthrough for whoever looks after it next.
What you keep at the end.
A container that's easy to read.
- Names that tell you what a tag does and where it sends data
- Triggers built on dataLayer events, not page layout
- No duplicate tags, and nothing firing that nobody can explain
- Consent checked on every tag that needs it
- Only the scripts the site needs, so pages stay fast
A way to keep it clean.
- A written naming convention, so new tags follow it
- One workspace per change, with version notes on every publish
- Publishing limited to the people who check
- A dataLayer request process, so developers know what to add and why
- QA standards for releases, so a site update can't quietly break tracking
Marc wrote tag governance, a dataLayer request process and QA standards for releases as Halfords documents.
Questions to ask any GTM consultant.
Whoever looks after your container, these questions show how careful the work will be. Here's how Marc answers them.
Will you audit before changing anything?
Yes. Every tag, trigger and variable is understood before anything is touched.
How do you test?
In a workspace, in Preview mode and on staging, across browsers, with consent granted and refused. Then checked against live data after publishing.
What happens to reporting while you work?
Changes go live in stages, so reporting keeps its continuity.
What will we be left with?
Documentation of the container, the event scheme and the dataLayer, and a walkthrough of how to make common changes safely.
Who will do the work?
Marc, himself. Agencies sometimes bring him in for exactly this part of a project.
Platforms and tools.
Websites.
Shopify, including checkout Customer Events, WooCommerce, Magento, Salesforce Commerce Cloud, Optimizely, WordPress and single-page apps built in React or Vue.
Destinations.
GA4, Google Ads and Floodlight, Meta, TikTok, Reddit and LinkedIn, including conversions API feeds, Infinity and ResponseTap call tracking, and HubSpot forms and meetings in the dataLayer.
Consent and server-side.
Consent Mode v2 with TagCommander or a custom banner, and server-side Tag Manager on Google Cloud or Stape.
Background.
- Ran all digital tagging through Google Tag Manager for VisitBritain's global marketing and ecommerce teams
- Delivered the move to GA4 across more than 50 Knight Frank websites using TagCommander and Tag Manager, with dataLayers generated from page metadata, so no market needed manual dataLayer upkeep
- As lead analytics consultant at Halfords, audited the GTM container (30 findings) and GA4 (48 checks), reassessed all 236 tags six months on, and made the case for rebuilding the container and dataLayer in the headless migration. The Halfords case study
- Server-side Tagging with Stape (2026) and Google Tag Manager Basics (2017)
More on the About page.
Case studies.
Straight answers.
What does a Google Tag Manager consultant do?
Audits, cleans up or rebuilds the container that runs your tracking, designs the dataLayer the site provides, and makes sure every tag sends the right data, at the right moment, with the right consent. Then documents it, so your team can change it safely.
How much does a GTM consultant cost?
A new Tag Manager setup is typically £800 to £2,500, a rebuild £1,200 to £3,500, and server-side GTM starts from £2,000. You get a fixed quote once the scope is agreed. The cost estimator adds up a whole project.
What is a GTM audit?
A line-by-line review of a Google Tag Manager container: what every tag sends, where, when and with what consent, plus duplicates, custom code, personal data and unused items. Findings are ranked by risk, with the cheap container-only fixes separated from work that needs developers.
How much does a GTM audit cost?
A first look at the container is part of the GA4 mini audit, from £175. A full container audit is quoted from the day rate, as containers vary so much in size: Halfords' had 236 tags.
How long does a GTM project take?
A straightforward build usually takes 2 to 3 weeks. Projects with server-side tagging, a large ecommerce setup or a lot of untangling can take 4 to 8 weeks. You get a realistic timeline after the first review.
Can you fix our container without breaking what already works?
Yes. The existing setup is audited before anything changes, every change is tested in Preview mode, and updates go live in stages so reporting keeps its continuity.
Can you take over a container an agency built?
Yes. It's audited first, so every tag, trigger and variable is understood before anything changes. Then it's cleaned up or rebuilt in stages, so reporting doesn't break while the work happens.
Do we need developer time?
Not always. At The Super Prime the whole ecommerce funnel was built in Tag Manager with zero back-end changes, live in under two weeks. A dataLayer the site writes is sturdier, though, and Marc writes the specification your developers build against.
What's the difference between client-side and server-side GTM?
Client-side GTM runs in the visitor's browser. Server-side GTM adds a container on your own cloud infrastructure, so data is collected first-party and you control what reaches each vendor. It still respects consent. The server-side GTM page covers when it's worth it.
Can you work on Shopify checkout?
Yes. Checkout no longer runs the Tag Manager snippet, so it's tracked with Customer Events alongside Tag Manager on the storefront, as for a direct-to-consumer Shopify retailer. Preview mode doesn't work at checkout, so changes go out in small, separately tested versions, as for Hertility Health.
Does Tag Manager slow the site down?
Tag Manager itself is light. What slows pages is what runs inside it: duplicate tags, heavy third-party scripts and custom code nobody remembers adding. Removing them is part of every clean-up.
Will our team be able to manage it afterwards?
That's the aim. Every project ends with documentation of the container, the event scheme and the dataLayer, plus a walkthrough of how to make common changes safely.
Do you work with agencies as well as in-house teams?
Both. Some agencies bring Marc in for the Tag Manager work on a client project; other clients are in-house marketing and analytics teams who want a Google Tag Manager expert.
Not sure what state your container is in? The GA4 mini audit checks it alongside GA4.
Last updated
Free tool
What does your site fire before consent?
Paste a page address. The tracking checker shows what a first-time visitor triggers before agreeing to anything, ranked by how much it matters.
Talk to Marc about it.
Tell Marc what's happening with your tracking. The quickest place to start is usually a GA4 mini audit: a prioritised list of what's broken and what to fix first.
Mini audit from £175.
Prefer to talk first? Choose "20-minute intro call" in the form.
Or email [email protected].