Mailchimp Site Tracking Pixel — Google Tag Manager template

A Google Tag Manager custom tag template that loads the Mailchimp Site Tracking pixel and forwards your site's GA4 ecommerce events to Mailchimp — no extra code on your site.

If you already send standard GA4 ecommerce events to the GTM dataLayer (view_item, add_to_cart, begin_checkout, purchase, …), this template turns them into the matching Mailchimp events automatically.

What it does

You add the tag once and give it your Mailchimp snippet URL. From then on:

• Standard GA4 ecommerce events are translated into Mailchimp events (for example add_to_cart → PRODUCT_ADDED_TO_CART, purchase → PURCHASED).
• The Google Analytics client ID is captured when you enable Capture Google Analytics Client ID (see Capturing the GA client ID), and sent to Mailchimp as a GOOGLE_CLIENT_ID identifier used to link a visitor across sessions during identity resolution.
• Optional hashed identifiers (email, phone) are captured when you enable them.
• Your own custom event names can be mapped to Mailchimp events without any code changes (see Custom event mappings).

The tag itself is a thin loader: it injects the Mailchimp pixel SDK and the SDK does all the work. Because the SDK reads the dataLayer directly, the tag only needs a single All Pages (Page View) trigger — you do not add per-event or ecommerce triggers.

Before you start

You'll need:

• A Mailchimp account with the Site Tracking integration set up (Mailchimp → Integrations).
• Admin access to a GTM container on your website.
• A site that already pushes GA4 ecommerce events to window.dataLayer.

Installation

1. Get your Mailchimp snippet URL

In Mailchimp, go to Integrations and open your site integration. You'll see a snippet like this:

<script id="mcjs">!function(c,h,i,m,p){m=c.createElement(h),p=c.getElementsByTagName(h)[0],m.async=1,m.src=i,p.parentNode.insertBefore(m,p)}(document,"script","https://chimpstatic.com/mcjs-connected/js/users/<USER_ID>/<CONNECTED_SITE_ID>.js");</script>

Copy just the URL from inside the script tag — the https://chimpstatic.com/mcjs-connected/js/users/…/….js part. That single URL is all the template needs.

You do not need to keep the raw snippet on your site. If you leave it installed alongside the GTM tag you may see double-tracking, so remove it before going live.

2. Add the template from the Community Template Gallery

1. In your GTM container, go to Templates → Tag Templates → Search Gallery.
2. Search for Mailchimp and select Mailchimp Site Tracking Pixel.
3. Click Add to workspace.

Prefer a manual install? You can also import template.tpl from this repository via Tag Templates → New → ⋮ → Import.

3. Create and trigger the tag

1. Go to Tags → New → Tag Configuration → Mailchimp Site Tracking Pixel.
2. Fill in:
   • Mailchimp snippet URL — the URL you copied in step 1.
   • Capture Google Analytics Client ID — enable to capture the GA4 client ID as a GOOGLE_CLIENT_ID identifier (see Capturing the GA client ID). On by default; uncheck to skip it.
   • GA4 Measurement ID — your G-XXXXXXXXXX. Required when capturing the client ID (see Capturing the GA client ID).
   • Capture and hash email (EMAIL_SHA256) — enable if your site pushes user_data.email to the dataLayer, or you map a User-Provided Data variable (see below).
   • Capture and hash phone (PHONE_SHA256) — enable if your site pushes user_data.phone_number to the dataLayer, or you map a User-Provided Data variable (see below).
   • (Optional) User-Provided Data variable — see Capturing user data.
   • (Optional) Custom event mappings — see below.
   • Read GA4 ecommerce events from the dataLayer — enabled by default; the SDK reads window.dataLayer to translate ecommerce events and capture user_data identifiers pushed alongside them. Disable only if your site's policy prohibits third-party dataLayer access — Capture Google Analytics Client ID and the User-Provided Data variable above still work with this off, since neither touches dataLayer.
3. Add a single trigger: All Pages (Page View). That's all that's needed — no per-event or ecommerce triggers. The injected SDK reads the dataLayer itself and translates ecommerce events on its own.
4. Save, then Submit / Publish the container.

Supported events

The template forwards these standard GA4 events out of the box:

GA4 event	Mailchimp event
view_item	PRODUCT_VIEWED
view_item_list	PRODUCT_CATEGORY_VIEWED
select_item	PRODUCT_VIEWED
add_to_cart	PRODUCT_ADDED_TO_CART
remove_from_cart	PRODUCT_REMOVED_FROM_CART
add_to_wishlist	PRODUCT_ADDED_TO_WISHLIST
view_cart	CART_VIEWED
begin_checkout	CHECKOUT_STARTED
add_payment_info	PAYMENT_INFO_SUBMITTED
purchase	PURCHASED
search	SEARCH_SUBMITTED

Page views are tracked automatically.

Required dataLayer shape

Push standard GA4 ecommerce events exactly as you would for GA4. The SDK reads event, ecommerce, (optionally) user_data, and search_term (for search) directly:

window.dataLayer = window.dataLayer || [];
dataLayer.push({ ecommerce: null }); // GA4 best practice: clear before each push
dataLayer.push({
  event: 'purchase',
  ecommerce: {
    transaction_id: 'tx-123',
    value: 59.98,
    tax: 4.50,
    shipping: 5.00,
    currency: 'USD',
    items: [
      { item_id: 'sku-1', item_name: 'Hat', price: 29.99, quantity: 2 }
    ]
  },
  user_data: {
    email: 'shopper@example.com',
    phone_number: '+1 (555) 123-4567'
  }
});

ecommerce.cart_id and ecommerce.checkout_id are optional. If present they're used as-is; otherwise the SDK generates and persists its own IDs in localStorage.

Capturing the GA client ID

When Capture Google Analytics Client ID is enabled, the pixel reads the GA4 client ID via Google's gtag('get', …) API and sends it to Mailchimp as a GOOGLE_CLIENT_ID identifier. Mailchimp uses it to link a visitor's activity across sessions during identity resolution — it is longer-lived than the pixel's own anonymous visitor ID, so it helps keep a contact resolvable over time.

• Requirements — your site must run GA4 on the page (gtag.js directly, or a GTM-managed Google tag) so gtag is available.
• Measurement ID — the pixel needs your GA4 Measurement ID (G-XXXXXXXXXX) to call gtag('get', …), so you must set the GA4 Measurement ID field explicitly — there is no auto-detection. Find it in Google Analytics under Admin → Data streams → your web stream. A Google Tag ID (GT-…) will not work; use the G-… Measurement ID.
• Consent-aware — capture goes through gtag, so when GA Consent Mode denies analytics storage, gtag returns no client ID and nothing is captured. There is no cookie fallback.
• Opt-in — capture only happens when the checkbox is enabled. When it's off (or the config is absent), the pixel does not attempt to read the client ID.
• Privacy — the GA client ID is an online identifier (personal data under GDPR, personal information under CCPA/CPRA). Before enabling, make sure your site's privacy notice discloses this use and your consent flow covers it.

Capturing user data

There are two ways to capture a customer's email/phone, both gated by the Capture and hash email/phone checkboxes:

1. From the dataLayer — if your site pushes a user_data object alongside your events (as shown above), the SDK reads user_data.email / user_data.phone_number directly.

2. From a GTM "User-Provided Data" variable — in some setups the email/phone is collected inside GTM and never reaches the dataLayer — so the SDK can't see it. In that case, create or reuse a GTM User-Provided Data variable and map it into the tag's User-Provided Data variable field so GTM passes the value to the SDK.

   The variable must resolve to an object with email and/or phone_number:

   { email: 'shopper@example.com', phone_number: '+1 (555) 123-4567' }

   GTM resolves the variable in the container when the tag fires and passes the value to the SDK, which normalizes and SHA-256 hashes it before sending (EMAIL_SHA256 / PHONE_SHA256). Only the fields whose capture checkbox is enabled are forwarded. Provide plaintext values — the SDK does the hashing, so don't map an already-hashed variable.

Custom event mappings

Some sites don't use the GA4-standard event names (for example a storefront that pushes addToCart instead of add_to_cart). The Custom event mappings table lets you map any dataLayer event name to a Mailchimp event without code changes. Each row has:

• Your dataLayer event name — the event string your site pushes (e.g. addToCart).
• Mailchimp event — the target event to fire.

Notes:

• Custom rows are added on top of the built-in mappings; the defaults keep working.
• If one event name resolves to more than one Mailchimp event, each one fires.
• Your custom event must still push GA4-shaped ecommerce data (and, for SEARCH_SUBMITTED, a top-level search_term); only the event name is remapped.
• You do not need to add a GTM trigger for your custom event name — the SDK reads it from the dataLayer.

Permissions used

Permission	Scope
logging	Debug environment only
access_globals	__mcGtmConfig (read/write)
inject_script	https://chimpstatic.com/mcjs-connected/js/users/*

The template only writes its settings to window.__mcGtmConfig and injects the Mailchimp pixel SDK from your snippet URL. Reading the dataLayer, hashing identifiers, and localStorage access all happen inside the SDK, not the template.

Testing

The template's unit tests live in the ___TESTS___ section of template.tpl and run inside the GTM template editor via Run tests.

To verify end-to-end, use GTM Preview mode: confirm the tag fires on page load (the All Pages trigger), the pixel SDK loads once from your snippet URL (Network tab), and your GA4 ecommerce events show up in Mailchimp (ecommerce analytics, segmentation, and automations).

License

Apache License 2.0 — see LICENSE.