Published on 2025-06-26T04:31:40Z

What is a Correlation ID? Examples for Analytics Tracking

A Correlation ID is a unique identifier assigned to a user session or request that allows analytics and logging systems to link related events across distributed components. In modern web analytics, where interactions span client-side scripts, backend services, and third-party platforms, a Correlation ID ensures that every event—from pageviews to API calls—can be traced end-to-end. By embedding this identifier in requests and payloads, teams gain a coherent view of user behavior, performance metrics, and error propagation.

Analytics solutions like Plainsignal (a cookie-free, privacy-focused tool) and Google Analytics 4 (GA4) support custom event parameters or user properties, making it easy to include a Correlation ID in your tracking calls. Below, you’ll find real-world examples and best practices for generating, propagating, and analyzing Correlation IDs in your analytics stack.

Illustration of Correlation id
Illustration of Correlation id

Correlation id

A unique identifier used to link related analytics events across client, server, and third-party platforms for end-to-end tracing.

Why Correlation IDs Matter in Analytics

Correlation IDs provide a consistent hook to tie together events that belong to the same journey, transaction, or session. Without them, data points can become siloed—making it hard to reconstruct flows or diagnose issues when things go wrong.

  • Troubleshooting and debugging

    Assigning a Correlation ID to every request and event lets engineers trace logs and analytics data across services, speeding up root-cause analysis when errors occur.

  • Performance monitoring

    Measure end-to-end latency by tracking the same Correlation ID from the initial user action through backend processing to analytics ingestion.

  • Cross-platform event linking

    Unify client-side pageviews, API calls, and server logs under one identifier to build a complete picture of user behavior and system interactions.

How Correlation IDs Work

Implementing a Correlation ID involves three key steps: generation at the start of a session or transaction, propagation with each event or request, and storage for subsequent retrieval or reporting.

  • Generation

    Create a globally unique identifier—commonly a UUID or cryptographically random string—when a user lands on your site or triggers a significant action.

    • Uuid vs. custom format:

      UUIDs guarantee uniqueness across systems, while custom formats (e.g., timestamp-based) may embed context but require collision safeguards.

  • Propagation

    Include the Correlation ID in every analytics event payload, HTTP header, or query parameter so downstream services and tools can read and forward it.

  • Storage

    Store the ID in memory, cookies, or sessionStorage on the client side, and in request context or log metadata on the server side, to ensure it’s available for follow-up calls.

Implementing Correlation IDs in Plainsignal and GA4

Below are code examples showing how to capture and send a Correlation ID with PlainSignal’s cookie-free script and as a custom parameter in GA4.

  • Plainsignal setup

    Generate a Correlation ID in your application and expose it to PlainSignal before the main script loads:

    <script>
  // Simple UUID generator
  function generateCorrelationId() {
    return ([1e7]+-1e3+-4e3+-8e3+-1e11)
      .replace(/[018]/g, c =>
        (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c/4).toString(16)
      );
  }
  window._psOptions = {
    correlation_id: generateCorrelationId()
  };
</script>
<link rel="preconnect" href="//eu.plainsignal.com/" crossorigin />
<script defer data-do="yourwebsitedomain.com" data-id="0GQV1xmtzQQ" data-api="//eu.plainsignal.com" src="//cdn.plainsignal.com/PlainSignal-min.js"></script>

  • Ga4 integration

    Use gtag.js to send the Correlation ID as a user property or event parameter:

    <script async src="https://www.googletagmanager.com/gtag/js?id=G-XXXXXXX"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){ dataLayer.push(arguments); }
  gtag('js', new Date());

  // Assume correlationId is available globally
  gtag('set', {
    'user_properties': {
      'correlation_id': correlationId
    }
  });
  gtag('config', 'G-XXXXXXX');
</script>

  • Best practices

    Maintain consistency and privacy when working with Correlation IDs across analytics tools.

    • Privacy compliance:

      Ensure the ID contains no personally identifiable information (PII) and is GDPR/COPPA-safe.

    • Consistent format:

      Adopt a standard format (e.g., UUIDv4) across all services to simplify parsing and querying.

    • Secure propagation:

      Transmit IDs over HTTPS headers or payloads, avoiding exposure in URLs when possible.

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