GTM Attribution Cookie (GTM Tag Template)

This Google Tag Manager (GTM) Custom Template sets a first-party cookie (and optionally localStorage) to capture and persist attribution data across pages and sessions. It captures UTM parameters and advertising Click IDs, formats them into a JSON object, and stores it for reuse in your tags, analytics tools, or backend systems. Optionally, it can push the same data into the dataLayer for GA4 and GTM workflows.

Built by Daniel Perry-Reed – analytics specialist at Data to Value.

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🚀 What This Does

• Captures UTM parameters:
  • utm_source, utm_medium, utm_campaign, utm_content, utm_term, utm_id, utm_source_platform, utm_creative_format, and utm_marketing_tactic
• Captures common ad click IDs gclid, fbclid and msclkid
  • Optionally add your own custom defined IDs
• Captures referrer info referrer.full and referrer.domain
• Stores attribution data in a first-party cookie
  • Optionally stores attribution in localStorage
  • Automatically syncs between cookie and localStorage if one is missing
• Optionally pushes attribution data to the dataLayer as a GTM event
• Optionally URL-encode all values
• Optioanlly logging all actions to the browser console

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✅ Changelog

Version	Changes
v0.1	- Initial release with support for core UTM parameters (utm_source, utm_medium, utm_campaign, utm_content, and utm_term) - Captured core click IDs (gclid, fbclid, msclkid) with option to add in custom list - Optional localStorage backup with cookie-localStorage sync functionality - Advanced options for overriding cookie settings - Optional browser console logs
v0.2	- Added support for additional UTM parameters (utm_id, utm_source_platform, utm_creative_format, utm_marketing_tactic) - Added optional DataLayer push feature (with configurable event name)
v0.3 (current)	- Added support for capturing referrer info (referrer.full and referrer.domain) - Added optional attribution update on referrers with no UTMs or Click IDs in the URL
future plans	- Optional custom mapping for traffic source/medium by click ID - TBC, let me know!

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🛠️ How to Use

📦 Option 1: Import the Prebuilt GTM Container

This is the fastest way to get started. It includes the custom template, tag, some dataLayer variables, and dataLayer trigger.

1. Download the container file
   📄 Download gtm_attr_container.json

2. Import into GTM

   • Go to GTM > Admin > Import Container
   • Upload the file
   • Choose your workspace
   • Select Merge and Rename conflicting tags/variables/templates

3. Review and publish

   • Confirm the tag fires as expected
   • Publish your container

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🛠️ Option 2: Manual Setup

1. Add the Custom Template

• Go to Templates > New
• Paste in the code from gtm_attr_template.js

2. Configure Template Fields

Field Name	Type	Description
cookieName	Text	Name of the cookie (default: gtm_attr)
cookieDomain	Text	Domain for the cookie (default: auto)
cookieHours	Text	Cookie lifetime in hours (default: 720)
extraClickIds	Text	Comma-separated custom click ID keys
encodeValues	Checkbox	URL-encode attribution values
enableLocalStorage	Checkbox	Store attribution in localStorage
pushToDataLayer	Checkbox	Push attribution object to dataLayer as an event
dataLayerEventName	Text	Event name for DataLayer push (default: gtm_attr)
overrideOnNewReferrerDomain	Checkbox	If enabled, JSON resets on new referrer domain (unless ignored)
ignoreDomains	Text	Comma-separated list of domains to ignore (no update if referrer matches)
logMessages	Checkbox	Enable console logging for debugging

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3. Set Template Permissions

Ensure your template requests:

• Set a cookie and Reads cookie value(s) (any)
• Access local storage (read/write for key gtm_attr)
• Access global variables (dataLayer read/write)
• getQueryParameters
• access_globals for dataLayer (read/write)
• Log to console (always log)
• Reads URL (any)
• Reads Referrer URL (any)

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4. Create the Tag

• Go to Tags > New
• Choose your custom template
• Set the trigger to All Pages or an appropriate consent-based trigger

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🧠 How Syncing Works

• When the tag fires:
  • If cookie is missing but localStorage exists, sync from localStorage to cookie
  • If localStorage is missing but cookie exists, sync from cookie to localStorage
• This ensures attribution continuity even if cookies are cleared while localStorage remains intact

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🔍 Example JSON Stored

Cookie / localStorage value:

{
  "utm_source": "google",
  "utm_medium": "cpc",
  "utm_campaign": "spring_sale",
  "utm_id": "12345",
  "utm_source_platform": "google_ads",
  "utm_creative_format": "responsive",
  "utm_marketing_tactic": "remarketing",
  "click_id": {
    "type": "gclid",
    "value": "abc123"
  },
  "referrer": {
    "full": "https://example.com/page",
    "domain": "example.com"
  }
}

DataLayer event (if enabled):

dataLayer.push({
  event: "gtm_attr",
  attribution: {
    ...same as above...
  }
});

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🟦 About Data to Value

Built and maintained by myself and the team at Data to Value — your data activation partner helping marketing and RevOps teams transform data into predictable revenue and growth.

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📄 License

MIT