Performancehighmetrics

Implement Google Consent Mode v2

rule · consent-mode

Google Consent Mode v2 is a mechanism that allows you to communicate your users' cookie or app identifier consent status to Google. Tags will adjust their behavior and respect users' choices.

Code Examples

This should be placed as high as possible in the <head>, before any GTM or gtag.js scripts.

HTML

<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
 
  // Default all to denied
  gtag('consent', 'default', {
    'ad_storage': 'denied',
    'ad_user_data': 'denied',
    'ad_personalization': 'denied',
    'analytics_storage': 'denied',
    'wait_for_update': 500
  });
</script>

When a user accepts cookies via your CMP (Consent Management Platform):

JavaScript

function onConsentAccepted() {
  gtag('consent', 'update', {
    'ad_storage': 'granted',
    'ad_user_data': 'granted',
    'ad_personalization': 'granted',
    'analytics_storage': 'granted'
  });
}

Why It Matters

Regulatory Compliance: Required for businesses operating in the European Economic Area (EEA) to comply with the Digital Markets Act (DMA).
Data Modeling: When users don't consent, Consent Mode uses conversion modeling to fill in the gaps, providing a more complete view of performance.
Privacy First: Respects user choices by ensuring that advertising and analytics cookies are only used when explicit consent is granted.
Functional Continuity: Allows basic measurement to continue even without personal data collection.

Validate the implementation with Google Tag Assistant (opens in a new tab) so you can confirm the consent state actually changes the requests sent after a user decision, not just the values stored in the page.

✅ Use a Certified CMP: Use a Consent Management Platform that is certified by Google to ensure correct implementation. ✅ Default to Denied: For users in the EEA, default consent states should be set to 'denied' until the user provides explicit consent. ✅ Update Promptly: Ensure the consent update is sent immediately after the user interacts with the consent banner. ✅ Verify with Tag Assistant: Use Google Tag Assistant to inspect pings and ensure the gcd and gcs parameters are correct.

❌ Don't Hardcode 'Granted': Never set consent to 'granted' by default for users in regulated regions. ❌ Don't Delay GTM Loading unnecessarily: Use the wait_for_update parameter instead of delaying the entire GTM script load.

Tools & Validation

Google Tag Assistant (opens in a new tab): Debugging tool to verify consent signals.
Chrome DevTools: Inspect network pings to google-analytics.com for the gcs and gcd parameters.
Tag Manager Debug Mode (opens in a new tab): View consent state changes in real-time.

Standards

Use web.dev: Learn Performance as the standard for measuring the final production behavior, not just local synthetic output.
Use Chrome Developers: Lighthouse overview as the standard for measuring the final production behavior, not just local synthetic output.

Verification

Automated Checks

Measure the affected page or flow in Lighthouse, PageSpeed Insights, or DevTools and confirm the targeted metric improves.
Inspect the network waterfall or performance timeline to confirm the intended resource or execution change actually took effect.

Manual Checks

Verify the change on a throttled mobile profile, not just local desktop.
If this rule maps to a budget or Web Vital, confirm the page now stays within that threshold.