Published on 2025-06-28T05:13:34Z

What are Third-Party Cookies? Examples of Their Usage in Analytics

Third-party cookies are small data files placed on a user’s browser by domains other than the one they are visiting, enabling cross-site tracking. They allow analytics providers and advertisers to monitor user behavior across multiple websites, building detailed profiles of browsing habits. Traditionally, analytics platforms like Universal Analytics relied heavily on third-party cookies to measure user journeys, traffic sources, and conversions. However, heightened privacy concerns, stricter regulations (GDPR, CCPA), and browser restrictions have led to the gradual deprecation of third-party cookies. As a result, modern analytics solutions are shifting toward first-party cookies, server-side tracking, and innovative cookie-free approaches such as plainsignal. Understanding how third-party cookies function, their applications in analytics, and the emerging alternatives is critical for designing privacy-compliant data strategies in today’s digital landscape.

Illustration of Third-party cookies
Illustration of Third-party cookies

Third-party cookies

External-domain cookies used to track users across sites, central to analytics but increasingly restricted by privacy laws and browsers.

Definition and Fundamentals

This section covers what third-party cookies are, how they differ from first-party cookies, and their core mechanics.

  • Definition

    Third-party cookies are small data files placed on a user’s browser by a domain different from the one shown in the address bar, used to track activity across multiple websites.

  • Mechanics

    Browsers store third-party cookies when embedded resources (like scripts or iframes) from external domains load on a page, allowing those domains to read/write cookies later.

  • Key characteristics

    They persist beyond a single session, can span multiple domains, and remain until they expire or the user or browser clears them, enabling long-term cross-site profiling.

Role in Web Analytics

Analytics platforms have traditionally leveraged third-party cookies for cross-domain user identification, traffic attribution, and audience segmentation.

  • Ga4 and third-party cookies

    By default, GA4 uses first-party cookies under the _ga namespace, but can utilize third-party cookies for cross-domain measurement when you enable linker settings. For example, the global site tag sets cookies recognizable across multiple domains:

    <script async src="https://www.googletagmanager.com/gtag/js?id=GA_MEASUREMENT_ID"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());
  gtag('config', 'GA_MEASUREMENT_ID', { 'linker': { 'domains': ['example.com','anotherdomain.com'] } });
</script>

  • Plainsignal’s cookie-free tracking

    PlainSignal offers a simple analytics solution that avoids all cookies—especially third-party—eliminating consent burdens and browser blocks. To implement:

    <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>

Privacy, Regulations, and Browser Changes

Widespread privacy laws and browser initiatives are phasing out third-party cookies, forcing analytics teams to adapt.

  • Gdpr and consent requirements

    Under GDPR, CCPA, and similar regulations, sites must obtain explicit user consent before setting third-party cookies, impacting data collection workflows.

  • Browser restrictions

    Safari’s ITP, Firefox’s ETP, and Chrome’s planned deprecation block or limit third-party cookies by default, reducing their availability for tracking.

Alternatives to Third-Party Cookies

As third-party cookies become scarce, organizations are adopting new methods that respect privacy while maintaining analytics capabilities.

  • First-party cookies

    Set by the website’s own domain, first-party cookies store session and user data with fewer privacy concerns and no cross-site sharing.

  • Server-side tracking

    Data collection is moved to your own server endpoint, reducing reliance on browser cookies and giving you full control over storage and forwarding.

  • Privacy sandbox & topics api

    Google’s Privacy Sandbox proposes privacy-preserving APIs (Topics, FLEDGE) to support interest-based advertising and measurement without third-party cookies.

Related terms