Unique reach measurement

Many content producers and advertisers want to know how many unique people saw their content. Use Shared Storage to record the first time a user saw your ad, embedded video, or publication, and prevent duplicative counting of that same user on different sites. You can then use the Private Aggregation API to output a summary report for your reach.

The Shared Storage API is a Privacy Sandbox proposal for general purpose, cross-site storage, which supports many possible use cases. Private Aggregation API is an output available in Shared Storage that lets you to aggregate cross-site data. To learn more about methods to implement these measurements, check out our reach whitepaper .

Try unique reach measurement

To experiment with unique reach measurement with Shared Storage and Private Aggregation, confirm you're using Chrome M107 or later. Enable all the Ad privacy APIs under chrome://settings/adPrivacy .

You can also enable Shared Storage with the --enable-features=PrivacySandboxAdsAPIsOverride,OverridePrivacySandboxSettingsLocalTesting,SharedStorageAPI,FencedFrames flag in the command line.

Experiment with code samples

You may want to keep track of how many unique users have seen your content across different sites. In this example, the content ID dimension is encoded into the aggregation key (bucket), and the count is used as the aggregatable value. The summary report will contain information such as "Approximately 391 users have seen the content ID 123."

In this example:

• unique-reach-measurement.js is loaded using a frame, and is responsible for loading the shared storage worklet.
• unique-reach-measurement-worklet.js is the shared storage worklet that checks the flag in shared storage and sends a report using the Private Aggregation API.

reach-measurement.js

  async 
  
 function 
  
 measureUniqueReach 
 () 
  
 { 
  
 // Load the Shared Storage worklet 
  
 await 
  
 window 
 . 
 sharedStorage 
 . 
 worklet 
 . 
 addModule 
 ( 
 'reach-measurement-worklet.js' 
 ); 
  
 // Run the reach measurement operation 
  
 await 
  
 window 
 . 
 sharedStorage 
 . 
 run 
 ( 
 'reach-measurement' 
 , 
  
 { 
  
 data 
 : 
  
 { 
  
 contentId 
 : 
  
 '1234' 
  
 } 
  
 }); 
 } 
 measureUniqueReach 
 (); 
 

reach-measurement-worklet.js

  // Learn more about noise and scaling from the Private Aggregation fundamentals 
 // documentation on Chrome blog 
 const 
  
 SCALE_FACTOR 
  
 = 
  
 65536 
 ; 
 function 
  
 convertContentIdToBucket 
 ( 
 contentId 
 ) 
  
 { 
  
 return 
  
 BigInt 
 ( 
 contentId 
 ); 
 } 
 class 
  
 ReachMeasurementOperation 
  
 { 
  
 async 
  
 run 
 ( 
 data 
 ) 
  
 { 
  
 const 
  
 { 
  
 contentId 
  
 } 
  
 = 
  
 data 
 ; 
  
 // Read from Shared Storage 
  
 const 
  
 key 
  
 = 
  
 'has-reported-content' 
 ; 
  
 const 
  
 hasReportedContent 
  
 = 
  
 ( 
 await 
  
 sharedStorage 
 . 
 get 
 ( 
 key 
 )) 
  
 === 
  
 'true' 
 ; 
  
 // Don't report if a report has been sent already 
  
 if 
  
 ( 
 hasReportedContent 
 ) 
  
 { 
  
 return 
 ; 
  
 } 
  
 // Generate the aggregation key and the aggregatable value 
  
 const 
  
 bucket 
  
 = 
  
 convertContentIdToBucket 
 ( 
 contentId 
 ); 
  
 const 
  
 value 
  
 = 
  
 1 
  
 * 
  
 SCALE_FACTOR 
 ; 
  
 // Send an aggregatable report using the Private Aggregation API 
  
 privateAggregation 
 . 
 contributeToHistogram 
 ({ 
  
 bucket 
 , 
  
 value 
  
 }); 
  
 // Set the report submission status flag 
  
 await 
  
 sharedStorage 
 . 
 set 
 ( 
 key 
 , 
  
 true 
 ); 
  
 } 
 } 
 // Register the operation 
 register 
 ( 
 'reach-measurement' 
 , 
  
 ReachMeasurementOperation 
 ); 
 

Engage and share feedback

Note that the Shared Storage API proposal is under active discussion and development and therefore subject to change.

We're eager to hear your thoughts on the Shared Storage API.

• Proposal: Review the detailed proposal .
• Discussion: Join the ongoing discussion to ask questions and share your insights.

Stay Informed

• Mailing List: Subscribe to our mailing list for the latest updates and announcements related to the Shared Storage API.

Need Help?

• Developer Support: Connect with other developers and get answers to your questions in the Privacy Sandbox Developer Support repository .