Making Sense of Your GA4 Data with Annotations and Anomaly Drivers 

Out with the new, in with the old. Google is reintroducing annotations in Google Analytics 4 (GA4). This returning feature has been rolled out to all GA4 users alongside another update called Anomaly Drivers. 

Welcome Back, Annotations 

Annotations were previously available in Universal Analytics, Google’s predecessor to GA4, and allowed users to add contextual notes to specific dates in reports and graphs. It’s super handy for tracking key events, like campaign launches, website updates, or tracking outages, and allows for more context-rich reports and analysis to be built. 

Existing annotations can be found in the “Annotations Viewer” (look for the post-in note icon in the top-right corner of reports) and adding a new annotation is as simple as right-clicking on a graph on your chosen date. Easy.

Why are annotations valuable for marketing teams? 

Annotations provide a range of benefits for marketing and analytics teams, including: 

• Recording the launch dates of significant marketing campaigns 

• Highlighting technical website issues that have affected data collection 

• Explaining irregularities in data trends 

• Building institutional knowledge within reports 

This feature was crucial in maintaining context alongside data during the Universal Analytics era. When the feature was removed, marketers had to find alternative ways to store and track key events. The return of annotations simplifies data interpretation and keeps valuable insights all in one place.

Introducing Anomaly Drivers 

Alongside annotations, Google has also rolled out a new GA4 feature called Anomaly Drivers — a machine learning-backed tool designed to help marketers understand why certain metrics have spiked, dipped, or gone off course. 

Instead of leaving you to piece together the puzzle, GA4 now automatically analyses the data behind these anomalies and highlights the most likely contributing factors. It builds comparison groups, surfaces trends, and suggests what’s driving the change. 

This means less time spent digging through secondary reports and more time spent acting on the insight. 

Let’s say your conversions drop off sharply over a weekend. Instead of guessing whether it was a bug, a broken form, or a campaign that ran out of budget — Anomaly Drivers might flag a drop in mobile sessions, a change in traffic source mix, or a sudden spike in bounce rate from a specific region. That’s the kind of context that helps you act quickly, communicate clearly, and avoid unnecessary panic. 

For marketers, this is especially useful when presenting data to internal teams or stakeholders who want not just the numbers — but the narrative behind them. Combined with annotations, Anomaly Drivers adds another layer of clarity, helping teams go beyond reporting and start telling the full story of their data. 

If your analytics setup needs refining, get in touch to learn how we can align your data strategy with your marketing strategy.