Google Tag Manager Integration with Magento 2

If you want to add Google Tag Manager without creating a module, you can add the gtm code from your active theme.

You can have two phtml templates to include the GTM snippet that needs to go to head and body.

// YourTheme/Magento_Theme/templates/html/gtm_head.phtml
<script>..</script> <!-- GTM code -->

// YourTheme/Magento_Theme/templates/html/gtm_body.phtml
<noscript>..</noscript> <!-- GTM code -->

You can use the default.xml file to load the above files.

<!-- YourTheme/Magento_Theme/layout/default.xml -->
<referenceBlock name="head.additional">
    <block class="Magento\Framework\View\Element\Template" name="gtm.head" before="-" template="Magento_Theme::html/gtm_head.phtml" />
</referenceBlock>

<referenceContainer name="after.body.start">
    <block class="Magento\Framework\View\Element\Template" name="gtm.body" before="-" template="Magento_Theme::html/gtm_body.phtml" />
</referenceContainer>

Usually I would recommend an extension because it allows you to pass additional data to the tag manager like product id, cart contents and placed orders.

But if you really just need it for this Facebook pixel and the Facebook pixel does not need page or session specific data, you can add the code with a static block, without touching the code:

1. create a static block (CMS > Static Blocks) that contains the script. You have to turn off the WYSWIWYG editor to enter JavaScript ("Hide Editor")

2. Create a new widget instance (CMS > Widgets) and select your theme

3. Add Layout Update for page "All Pages" and reference "Page Top" (this is a container directly after the opening body tag)

4. Select static block from (1) in "Widget Options":

5. Save.

6. Clean cache.

Note that editing JavaScript in a static block does not work well. You can save it once, but when you want to edit the block, the script will be crippled by the WYSIWYG editor and you'll have to add it again from scratch. If it's an option for you to add a template file to the theme instead, you can do it like this:

1. create a file app/design/frontend/[your package]/[your theme]/template/page/gmt.phtml that contains the HTML snippet for the Google Tag Manager

2. create the static block as above, but with the following content

   {{block type="core/template" template="page/gmt.phtml"}}
   

3. Add "core/template" to the block whitelist in System > Permissions