Third-Party Cookies: Complete Guide for Digital Marketing

Third-party cookies have become a central topic in online advertising. They are essential tools that enable campaign measurement and personalization across the web. At the same time, cookie functionality, usage, and limitations are constantly being reshaped by regulations and browser decisions.

In this article, we'll explore what third-party cookies are, how they work, and how to manage them in light of new privacy regulations.

What Are Third-Party Cookies?

Third-party cookies are files saved in your browser by domains different from the website you're visiting, primarily used for cross-site tracking, advertising, and measurement. For this reason, their compliance with privacy and data security regulations is at the center of many debates today, especially after Google and other search engines adopted changes and alternative solutions like the Privacy Sandbox.

Unlike first-party cookies, which belong to the domain you're browsing, third-party cookies originate from third-party domains embedded in the page and have broader implications for privacy, consent, and data governance in Europe under GDPR and ePrivacy.

The commonly adopted macro-categories include technical or necessary cookies, functional cookies, analytical/marketing cookies, and profiling cookies, with third-party cookies potentially falling into multiple categories depending on their purpose and the domain that sets them.

Technical or necessary cookies enable basic functions like sessions and essential preferences and don't require consent, positively impacting UX but with minimal privacy impact. In contrast, functional cookies improve the experience without extensively profiling the user. Analytics and marketing cookies, often third-party, measure behavior and performance and can contribute to targeted advertising, while profiling cookies track cross-site to create segments, requiring explicit consent and transparency about their purposes.

First-Party Cookies

First-party cookies are created by the visited domain and are generally under the direct control of the site owner, making them simpler to configure and manage. They improve user experience on the site by remembering logins, preferences, and shopping carts, supporting first-party analytics and reducing risks of unnecessary sharing with third parties. They remain subject to different rules based on their purpose: if used for profiling they require consent, if technical they don't.

Second-Party Cookies

By "second-party" we typically mean first-party data shared between partners in direct agreements, not a technical category of the cookie protocol, but a data exchange model that sometimes emulates third-party cookie capabilities in controlled contexts. This practice can occur through server-side integrations or clean rooms, where first-party data is combined while respecting consent and with minimization measures. The UX impact can remain neutral if transparent, while privacy depends on the perimeter and the control and audit mechanisms.

Third-Party Cookies

Third-party cookies are set by domains different from the visited site, often through advertising tags, pixels, or widgets, and enable cross-site tracking, retargeting, and multi-touch measurement. They have a significant privacy impact due to their cross-domain nature and require particular attention to consent, information notices, and governance with management tools (CMPs). User experience can suffer from banners and consent choices, but they enable more relevant advertising experiences when the user consents.

Technical Cookies vs Profiling Cookies

Technical or strictly necessary cookies enable basic operational functionalities and don't need consent, while profiling cookies serve to create profiles for personalized advertising and require explicit and documented consent.

Profiling cookies can be first-party or third-party, with third-party more oriented to cross-site scenarios and therefore more invasive for privacy. Italian guidelines reiterate the requirement of granular consent for categories and prohibition of dark patterns in banners.

First-Party vs Third-Party Cookies: Three Practical Differences

Regarding control and data ownership, first-party cookies are managed by the site owner with greater governance, while third-party cookies are managed by external providers who become autonomous controllers or processors depending on their role, requiring agreements and transparency. On reading scope, first-party cookies are readable only by the origin domain, third-party by third-party domains on different sites, enabling cross-domain use. For tracking and consent, third-party cookies activated for profiling require explicit and recorded consent, with CMPs and clear information about purposes and duration.

How They're Created and Technologies That Generate Them

Operationally, third-party content loaded on the page makes an HTTP request to the provider's domain which can respond with a Set-Cookie header, saving the cookie in the browser in a third-party context, then readable in subsequent calls to the same domain.

The ecosystem includes tag managers, ad servers, CDNs, social widgets, and conversion pixels that inject scripts and resources capable of setting or reading cookies according to browser policies and attributes like SameSite. There are differences between cookies set client-side via JavaScript and server-side via HTTP headers, with implications for security, attributes, and modern browser restrictions.

Why Third-Party Cookies Are Essential in Digital Marketing

In digital marketing, third-party cookies enable retargeting, personalization, and audience building, improving CTR and conversions through consistent messaging along the funnel. They allow cross-site measurement and multi-touch attribution, connecting impressions, clicks, and conversions across different domains to estimate ROI and user journeys. They support frequency capping and viewability, limiting excessive exposures and optimizing inventory quality to benefit advertisers and DSPs.

Use for Retargeting and Personalization

Retargeting recognizes visitors on partner sites and shows ads based on previous interactions, reducing waste and increasing relevance with persistent third-party identifiers. Dynamic ad personalization can update creatives based on detected cross-site events, improving performance over generic messages.

Cross-Site Measurement and Attribution

Third-party cookies connect events across multiple domains and platforms, helping build journeys and attribution models that reflect contributions from different touchpoints. Without these signals, measurement tends to fragment and depend on probabilistic models or aggregated signals.

Frequency Capping and Viewability

Limiting the number of impressions per user, reducing fatigue, and improving efficiency is a function often based on cookies shared between sites and ad servers. Viewability integrates with identifiers to optimize delivery toward more effective placements.

Key obligations include explicit consent for profiling cookies, complete information on purposes and duration, granular management of preferences, and recording choices through CMPs. Users must be able to refuse with equal ease compared to acceptance, without dark patterns, and modify preferences at any time. Transparency about third parties involved and SDKs/tags used is an essential part of the information notice.

Consent is necessary for all non-strictly necessary cookies, including profiling and many forms of analytics and marketing, especially if third-party or if they process personal data for advertising purposes. Exceptions for analytics are limited and require configurations that don't allow direct user identification and aggregated data, varying depending on the Data Protection Authority's interpretation.

The information notice must describe categories, purposes, duration, third parties, legal basis, and methods to revoke consent, linking to a compliant banner and granular preferences. It's appropriate to include references to tools used and links to third-party provider policies.

CMPs allow consent collection and recording, presentation of compliant banners, and integration with tags for conditional firing based on user choices. They support audits and proof of consent, reducing sanctioning risks and improving governance.

How to Verify if a Site Uses Third-Party Cookies

To verify via browser, open DevTools, Application section to list cookies by domain, and Network section to inspect responses and Set-Cookie headers from calls to third-party domains. Checking domains loaded in the Network tab helps identify external sources like ad servers, CDNs, pixels, and widgets that can set cookies.

Automated tools and online scanners can map categories and third parties, but should be interpreted considering consent state and local configurations.

Browser Verification (Chrome/Firefox/Safari)

Chrome, Firefox, and Safari offer panels to view cookies by origin and details on attributes like SameSite, Secure, and HttpOnly, useful for distinguishing first-party and third-party contexts. Safari has strongly limited third-party cookies for years, affecting inspection results compared to Chrome.

Automated Tools and Scanners

Solutions like compliance scanners and CMP reports list detected cookies and related legal bases, with reports useful for audits and technical remediation. Output should be manually verified on key pages and different consent states.

Interpreting Results

The presence of cookies with a domain different from the site indicates third parties; correlating their set with events and tags helps reconstruct purposes and data paths. Check duration, path, and attributes to assess privacy risk and consent necessity.

How to Block or Allow Third-Party Cookies (Browser Guide)

On Chrome, you can enable or disable third-party cookies from privacy and security settings, with granular controls for sites and browsing modes. Firefox and Safari offer advanced protections that block many third-party cookies by default, with options for whitelists or exceptions. On iOS and Android, default browser settings and specific app settings determine behavior, with the possibility of relying on extensions or plugins where allowed.

Enabling Third-Party Cookies in Chrome

Chrome allows managing third-party cookies for all sites or selective exceptions, considering updated policies communicated in the Privacy Sandbox context. Users can choose balances between personalization and privacy at profile or session level.

Disabling Third-Party Cookies on Mobile

Many mobile browsers include default blocks or options to limit third-party cookies, with differences between WebView, Safari iOS, and Chrome Android. Checking app settings and exceptions for trusted sites allows maintaining essential functionalities.

Using Browser Privacy Settings

Privacy sections also allow deleting cookies by category and period, controlling tracking and preventing fingerprinting, with varying impacts on site compatibility. A balanced configuration minimizes UX friction while maintaining data control.

Alternatives to Third-Party Cookies (Cookieless Approaches)

Strategies based on first-party data, contextual targeting, server-side tracking, clean rooms, and alternative consent-based identifiers offer sustainable and compliant paths. Aggregated signals and cohorts, along with hashed emails with consent, can support measurement and activation without non-consensual cross-site identifiers. Avoiding invasive techniques like fingerprinting without consent remains an essential ethical and compliance note.

Contextual Targeting

Contextual targeting uses page content and in-page signals to show relevant ads, reducing dependence on user IDs. It improves privacy by design and can achieve good performance with curated creatives and taxonomies.

First-Party Data Strategy

Collecting data with clear value exchange, like preferences and intent, and activating it in proprietary environments or controlled partnerships is central in the cookieless era. Consent quality and data governance determine reliability and scalability.

Server-Side Tracking and Clean Rooms

Server-side tracking reduces client signal loss, improves control and security, and integrates with clean rooms for anonymous matching and aggregated measurements. These approaches require technical investments but preserve measurement and activation in a compliant manner.

Impact on AdTech Ecosystems and Advertisers

The reduction of third-party cookies pushes DSPs, SSPs, and DMPs toward first-party signals, probabilistic modeling, and aggregated data, changing targeting and frequency logic. Programmatic campaigns adopt a mix of contextual, consent-based IDs, and algorithmic optimization with less reliance on cross-site identifiers. AI's ability to infer propensities from non-deterministic signals becomes key to performance in cookieless environments.

Adapting DSP Strategies

DSPs value inventory with first-party signals, prioritize S2S integrations, and support cohorts/interest groups when available, reducing third-party dependencies. Bidding models increasingly incorporate contextual and predictive signals.

In particular, ad:personam, our Self-Service DSP for programmatic marketing, allows clear and intuitive cookie management.

Measurement and Attribution Without Cookies

The shift is toward models based on conversion modeling, incrementality, and aggregated measurements, with more use of experiments and clean rooms. Attribution windows shorten and the importance of first-party analytics grows.

Role of AI in Cookieless Solutions

AI algorithms fill identification gaps with pattern recognition and propensity estimates, respecting privacy limits when trained on consensual and aggregated data. Dynamic creative optimization leverages in-page and contextual signals more than persistent profiles.

Technical Implementation for Developers and AdOps Teams

Reducing dependence on third-party cookies involves moving toward server-side events, correctly setting SameSite, Secure, and HttpOnly attributes, and configuring tag managers for consent-conditional firing. Adopting S2S pipelines for conversions and audiences and integrating with CMPs for call gating is now baseline. Server-side modeling compensates for missing signals and improves data quality for proprietary analytics.

Server-Side Tracking Basics

Collecting events on the brand's server limits identifier exposure in the client and centralizes controls, with mapping toward partners respecting consent. It reduces impacts of ITP/ETP and ad blockers on measurement.

Configuring SameSite and Secure

Setting SameSite=Lax/Strict avoids unwanted cross-site access while None; Secure is necessary for third-party context on HTTPS, according to modern browser policies. Correct attributes reduce risks and tracking inconsistency.

Best Practices for Tag Management

Aligning firing with CMP choice, reducing tag duplications, documenting third parties, and relating changes is essential for compliance and performance. Periodic testing in different environments and with simulated consent states prevents leakage.

Monitoring impressions, CTR, conversion rate, and cookieless traffic share helps assess the effect of third-party cookie loss on performance. Multi-touch attribution KPIs, user identity loss, and audience quality indicate how effective alternatives like contextual and first-party are. Segmenting reports by browser, consent state, inventory, and consent ID presence offers visibility on where to intervene.

KPIs for Advertisers

Observing CPA/ROAS variations for segments with and without IDs allows calibrating budget and tactics. Incrementality testing helps distinguish credit shifts from real lift.

KPIs for Platforms/DSPs

For platforms, ID coverage, effective capping, and match rates on consensual signals become health indicators. Model stability with aggregated signals is another fundamental KPI.

Interpreting Variations After Cookieless Transition

Expecting precision drops in retargeting and MTA and increasing the weight of incremental and cohort models is physiological. Success depends on creativity, context, and proprietary data quality.

Best Practices for Site and Marketing

Clarifying consent value exchange, collecting first-party data with valuable experiences and content, and optimizing landing pages for conversions even without cross-site history are fundamental steps. For example, quality SEO work reduces dependence on cookie identifiers, while continuous A/B testing improves performance over time. Documenting third parties and regularly updating the cookie policy maintains compliance and trust.

First-Party Collection and Use

Clear forms, offers, and loyalty programs with well-explained consent build reliable and actionable datasets. Consent governance and data minimization are central elements.

Educating on why data matters and how it improves experience increases opt-in rates and reduces informed refusals. Avoiding banner friction improves brand perception and compliance.

Testing and Optimization

Testing creatives, context, pages, and conversion paths replaces part of the historical advantage of persistent profile. Analysis by browser segment and consents allows continuous fine-tuning.

Frequently Asked Questions About Third-Party Cookies (FAQ)

Question 1: What are third-party cookies?

Third-party cookies are small files stored in the user's browser by domains different from the site they're visiting. They're primarily used to track browsing behaviors across multiple sites, enable personalized advertising campaigns, and improve measurement of digital campaign performance. On ad:personam, third-party cookies help the DSP platform optimize targeting and ad distribution through artificial intelligence systems, allowing users to manage their campaigns autonomously without minimum spend requirements.

Question 2: How are cookies divided?

Cookies can be divided into different categories based on function and origin. The main ones are: first-party cookies, created by the visited site and used to improve user experience; second-party cookies, shared between direct partners; and third-party cookies, generated by external domains for tracking, advertising, and analysis purposes. Other classifications include technical, functional, profiling, and marketing cookies, each with specific usage and management methods.

Question 3: What happens if we choose to block third-party cookies in our browser?

Blocking third-party cookies limits the ability of external domains to track navigation across multiple sites, reducing personalization of advertising and precision of programmatic campaigns. On platforms like ad:personam, this means some targeting and automatic optimization functions based on cross-site data may be less effective, while user privacy is strengthened. Users can still continue to manage and create campaigns, leveraging first-party data and other cookieless techniques supported by the platform.

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