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Installing Google Tag Manager on a PrestaShop store

Google Tag Manager on PrestaShop means a container added once to the theme, after which every tag, GA4, Ads, Meta, is managed from the GTM interface with no new deployment. The prerequisite I install alongside it is a data layer fed by PrestaShop, or GTM has nothing to read.

Describe my issue Send a message

The situations I handle

  • You keep adding marketing tools and have to edit the theme every time
  • GTM is installed but no tag fires correctly
  • You’re not sure where to cleanly place the container’s two code snippets
  • PrestaShop’s data layer is empty or incomplete on the cart and checkout
  • Several people work on the site and the tracking code is duplicated in several places

How I install GTM on PrestaShop

  1. Creating the GTM container

    I create the container in the Google Tag Manager interface, which generates two code snippets: one for the head, one for right after the body tag opens.

  2. Placing it in the PrestaShop theme

    I place the first snippet in the theme’s head.tpl file, just before the closing </head>, and the second in the displayAfterBodyOpeningTag hook rather than hard-coded in a file copied onto every page.

  3. Building the data layer

    I have PrestaShop push product, cart and order variables (items, value, currency, transaction_id) at the right moment on the product page, cart and order-confirmation page, so GTM has data to read.

  4. Adding tags from the GTM interface

    Once the data layer is in place, I add GA4 and other marketing tags directly in GTM, without going back into the theme code.

  5. Testing in preview mode

    I check, page by page, which tags fire and with which data layer variables, before publishing the container to production.

Why go through GTM instead of hard-coding every tag

Without a tag manager, every new marketing tool, a Meta pixel, a Google Ads tag, means editing the PrestaShop theme and clearing the cache. With GTM, a single container is added once, and every following tag is managed from the interface, with no new deployment.

The container alone isn’t enough: GTM reads a data layer, a JavaScript data layer that PrestaShop needs to feed with product, cart and order information at the right time. Without a structured data layer, the ecommerce tags set up in GTM have nothing to read, even if the container itself is installed correctly.

I prefer placing both code snippets through theme files and PrestaShop’s native hooks rather than hard-coded across several copied templates, to keep a single point of maintenance.

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Frequently asked questions

Does the GTM container replace Google Analytics 4?
No, GTM is a tag manager. GA4 is still the measurement tool: it’s set up as a tag inside the GTM container once that’s installed.
Can I install GTM and gtag.js at the same time?
No: GA4 then gets loaded twice and every event is sent in duplicate. I pick one method or the other, never both on the same site.
Do I need a PrestaShop module to install GTM?
A module can simplify placing the two code snippets, but I mostly work directly through theme files, to keep control over the exact location and avoid clashing with other tracking modules.
How do I check PrestaShop’s data layer is properly fed?
Google Tag Manager’s preview mode shows the data layer’s content on every page as a tag fires, making it easy to spot straight away if a variable like value or transaction_id is empty.
Do I need visitor consent before GTM fires tags?
GTM itself collects nothing: it’s the tags it fires, GA4, Ads, Meta, that are concerned. GA4, in its standard configuration, doesn’t meet the CNIL’s exemption criteria and therefore, in principle, requires the visitor’s prior consent.

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