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Intercepting GA4 events

This guide covers methods for intercepting Google Analytics 4 (GA4) events. Choose the method that best fits your needs.

Methods 1 and 2 are for web tracking with client-side GTM, Method 3 is for web tracking with direct gtag (no GTM), and Method 4 is for server-side tracking (server-side GTM).

This method keeps your existing GA4 setup intact while duplicating events to a custom endpoint. Your data will continue flowing to Google Analytics as normal.

Steps:​

  1. Open Google Tag Manager

    • Navigate to your GTM container
    • Go to the Tags section

  2. Create a Custom HTML Tag

    • Click New to create a new tag
    • Choose Custom HTML as the tag type
    • Name it: D8A GA4 Duplicator

  3. Add Your Interception Code

    • Paste your custom code generated below into the HTML field
note

The duplicator copies GA4 tracking requests to your endpoint while keeping the original Google Analytics requests intact. It does this by intercepting common request mechanisms (XMLHttpRequest, fetch, navigator.sendBeacon, and script src assignments).

Use the minified snippet for production, or the non-minified version for auditing. You can also review the full implementation in the source code.

You will find it in the d8a Cloud dashboard.
Optional: Use the button below to route specific GA4 Measurement IDs to different endpoints.

  1. Save the tag

    • Save your D8A GA4 Duplicator tag so it is available when you configure the Google Tag in the next step
    • Note: You do not need to add a trigger to this tag

  2. Fire the duplicator before the Google Tag

    • Open your Google Tag (your GA4 configuration tag)
    • Expand Advanced Settings → Tag Sequencing
    • Under Fire a tag before Google Tag Name fires, select your D8A GA4 Duplicator tag

  3. Save and Publish

    • Save your tag
    • Submit the changes and publish your container

You can now test your web tracking setup.

Method 2: Redirect all GA4 requests in GTM​

⚠️ Warning: This method will stop sending data to your GA4 property. Use only if you want to completely redirect tracking to your d8a instance.

Steps:​

  1. Open Google Tag Manager

    • Navigate to your GTM container
    • Go to the Tags section

  2. Modify Your Google Tag

    • Find your existing Google Tag (GA4 Configuration tag)
    • Edit the tag configuration

  3. Change the Server Container URL

    • In the tag Configuration settings, add a new parameter called server_container_url
    • Set its value to your d8a tracking domain, e.g. https://example.org/
      note

      Google automatically appends /g/collect to this value, so do not include /g/collect in server_container_url.

Method 3: Duplicate GA4 requests with gtag directly​

This method duplicates requests at the Google Tag (gtag) level by adding service_container_url as an additional destination.

note

This method assumes gtag is already installed directly in your HTML (without web GTM).

Steps:​

  1. Confirm your direct gtag setup

    • Verify the standard Google tag snippet is already present in your page (for example, in <head>)

  2. Keep your existing GA4 config call

    • Leave your primary gtag('config', 'G-XXXXXXX') call unchanged

  3. Add a second config call with service_container_url

    • Add another gtag('config', ...) call for the same Google tag ID
    • Set service_container_url to your d8a endpoint URL, for example: https://global.t.d8a.tech/13370000-1984-0042-0069-c0ffee123456/g/collect
    • Example:
<script
  async
  src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXXX"
></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag() {
    dataLayer.push(arguments);
  }
  gtag("js", new Date());

  // Existing GA4 destination
  gtag("config", "G-XXXXXXX");

  // Additional destination for duplicated traffic
  gtag("config", "<property_id>", {
    service_container_url: "https://global.t.d8a.tech/<property_id>/g/collect",
  });
</script>

Testing your web tracking setup​

  1. Open Browser DevTools

    • Go to Network tab
    • Filter by "collect" or your endpoint domain

  2. Trigger Test Events

    • Navigate pages, click buttons, submit forms
    • Watch for outgoing requests

  3. Verify Data Flow

    • Method 1: Check both GA4 and your endpoint receive data
    • Method 2: Check only your endpoint receives data
    • Method 3: Check GA4 traffic is duplicated to your service_container_url endpoint

  4. Optional: Use GTM Preview Mode (Methods 1 and 2 only)

    • Enable Preview mode in GTM
    • Verify tags fire in the correct sequence
    • Check for any errors in the console

Method 4: Duplicate requests in Google Tag Manager server-side​

This method duplicates GA4 requests at the server-side container level, which is useful for server-side tracking implementations.

note

This method assumes you already have a working GA4 client configured in your Google Tag Manager server-side container. If you haven't set up server-side GTM yet, please configure your GA4 client first.

Steps:​

  1. Create a User-Agent Variable

    • Go to Variables in your server-side GTM container
    • Click New to create a new variable
    • Choose Request Header as the variable type
    • Set the Variable Name to: User-Agent
    • Set the Header Name to: User-Agent
    • Save the variable

  2. Create an X-Forwarded-For Variable

    • Create another new variable
    • Choose Request Header as the variable type
    • Set the Variable Name to: X-Forwarded-For
    • Set the Header Name to: X-Forwarded-For
    • Save the variable

  3. Add the JSON HTTP Request Tag Template

    • Go to Templates in your server-side GTM container
    • Click Search Gallery
    • Search for and add the JSON HTTP request tag template from the community gallery

  4. Create a New Tag

    • Go to Tags and click New
    • Choose the JSON HTTP request tag template you just added
    • Configure the tag:
      • Destination URL: <your-d8a-instance-url>{{Request Path}}?{{Query String}}
        • Replace <your-d8a-installation-url> with your d8a endpoint URL (e.g., https://example.org)
        • For example, your completed Destination URL should look like:
          https://example.org{{Request Path}}?{{Query String}}
          note

          {{Request Path}} and {{Query String}} are built-in variables available in server-side GTM.

    • In the Request Headers section, add two entries:
      • First entry:
        • Key: User-Agent
        • Value: {{User-Agent}}
      • Second entry:
        • Key: X-Forwarded-For
        • Value: {{X-Forwarded-For}}

  5. Configure the Trigger

    • In the Triggering section, select the same trigger that you use for your GA4 traffic. This ensures the tag fires whenever GA4 events are processed

  6. Save and Publish

    • Save your tag
    • Submit the changes and publish your server-side container

Testing your server-side tracking setup​

To test your server-side setup, use the debug mode in Google Tag Manager server-side. This enables you to verify that requests are duplicated correctly to your d8a endpoint. The final URL and d8a server response will be available in the Console tab.

Prefer a native tracker instead?​

If you do not want to intercept existing GA4 tracking and prefer a setup that is independent from Google, use our dedicated gtag-compatible web tracker: Web tracker.