K+ frequency measurement

Use Shared Storage and Private Aggregation for K+ frequency measurement

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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 allows you to aggregate cross-site data.

Try K+ frequency measurement

To experiment with K+ frequency measurement with Shared Storage and Private Aggregation, confirm you're using Chrome M107 or later. Then enable the Privacy Sandbox Ads APIs experiment flag at chrome://flags/#privacy-sandbox-ads-apis.

Set Privacy Sandbox Ads APIs experiment to enabled to use these APIs

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

Experiment with code samples

The following code samples were created to demonstrate how the API may be used for the given use cases. These are not meant to be used in production.

You may want to measure the number of users who have seen your content K or more times a given client across different sites. In this example, the impression count is added to shared storage where it increments by 1 whenever the content is loaded. When the impression count has reached 3, the Private Aggregation API is called. The content ID dimension is encoded as the aggregation key, and the count is used as the aggregatable value. The summary report will provide information such as "Approximately 391 users have seen the ad campaign ID 123 at least 3 times."

In this example:


async function injectContent() {
// Load the Shared Storage worklet
await window.sharedStorage.worklet.addModule('k-freq-measurement-worklet.js');

// Run the K-frequency measurement operation
await window.sharedStorage.run('k-freq-measurement', { data: { kFreq: 3, contentId: 123 });



// Learn more about noise and scaling from the Private Aggregation fundamentals
// documentation on Chrome blog
const SCALE_FACTOR = 65536;

* The bucket key must be a number, and in this case, it is simply the content
* ID itself. For more complex bucket key construction, see other use cases in
* this demo.

function convertContentIdToBucket(contentId) {
return BigInt(contentId);

class KFreqMeasurementOperation {
async run(data) {
const { kFreq, contentId } = data;

// Read from Shared Storage
const hasReportedContentKey = 'has-reported-content';
const impressionCountKey = 'impression-count';
const hasReportedContent = (await this.sharedStorage.get(hasReportedContentKey)) === 'true';
const impressionCount = parseInt((await this.sharedStorage.get(impressionCountKey)) || 0);

// Do not report if a report has been sent already
if (hasReportedContent) {

// Check impression count against frequency limit
if (impressionCount < kFreq) {
await this.sharedStorage.set(impressionCountKey, impressionCount + 1);

// Generate the aggregation key and the aggregatable value
const bucket = convertContentIdToBucket(contentId);
const value = 1 * SCALE_FACTOR;

// Send an aggregatable report via the Private Aggregation API
privateAggregation.sendHistogramReport({ bucket, value });

// Set the report submission status flag
await this.sharedStorage.set(hasReportedContentKey, 'true');

// Register the operation

register('k-freq-measurement', KFreqMeasurementOperation); \

Use cases

These are only some of the possible use cases for Shared Storage. We'll continue to add examples as we receive feedback and discover new use cases.

Content selection

Select and display different content on different websites in fenced frames based on information collected in Shared Storage. The output gate for these use cases is URL selection.

  • Creative rotation: Store data, such as creative ID, view counts, and user interaction, to determine which creative users' see across different sites.
  • A/B testing: You can assign a user to an experiment group, then store that group in Shared Storage to be accessed cross-site.
  • Custom user experiences: Share custom content and calls-to-action based on a user’s registration status or other user states

Generate summary reports

Collect information with Shared Storage and generated a noisy, aggregated summary report. The output gate for these use cases is the Private Aggregation API.

  • 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.
  • Demographics measurement: Content producers often want to understand the demographics of their audience. You can use Shared Storage to record user demographic data in a context where you have it, such as your first-party site, and use aggregated reporting to report on it across many other sites, such as embedded content.
  • K+ frequency measurement: Sometimes described as "effective frequency," there is often a minimum number views before a user will recognize or recall certain content (often in the context of advertisement views). You can use Shared Storage to build reports of unique users that have seen a piece of content at least K number of times.

Engage and share feedback

The Shared Storage proposal is under active discussion and subject to change in the future. If you try this API and have feedback, we'd love to hear it.

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