If you’ve ever tried to extract client or session IDs from Google Analytics cookies in Google Tag Manager, you know it hasn’t been easy. Developers were forced to reverse-engineer the _ga cookie format, write fragile code, and hope nothing changed overnight. Spoiler alert: it often did.
Introducing readAnalyticsStorage
Google Tag Manager now supports a new sandbox API in custom templates: readAnalyticsStorage. This API provides direct, safe access to Google Analytics' client and session data.
Why it matters
- Future-proof: The API abstracts away cookie format changes.
- Reliable: You get guaranteed structure and values.
Try the Demo Template
I’ve built a simple demo GTM custom template that uses this API. It reads and logs GA identifiers. Here's a quick look at the code:
const readAnalyticsStorage = require('readAnalyticsStorage');
const log = require('logToConsole');
const analyticsStorageData = readAnalyticsStorage();
log('Analytics storage data:', analyticsStorageData);
if (!analyticsStorageData) {
log('Data unavailable or user declined analytics storage.');
return undefined;
}
return analyticsStorageData;GTM Preview: Output of Variable Using readAnalyticsStorage
Conclusion
If you’re using GTM to power analytics or marketing tags, this API is a must-use for cleaner, safer, and more maintainable setups. Try the demo template, explore the API, and future-proof your data collection today. Get your hands dirty with the new readAnalyticsStorage API check out the release notes or reach out to me if you need help getting started!