What is Cookie Syncing? How Does it Optimize Ad Campaigns?

Here’s a scenario: a customer is browsing online for a particular item and maybe even puts it into their shopping cart for later. The next time they open their browser, lo and behold, there’s an advert for that same product—a gentle nudge to finalize their purchase. This reminder is made possible by cookie syncing. Advertisers exchange user data so you can target audiences with more relevant ads.

But how does cookie syncing work? How does it optimize programmatic ad campaigns? And what are the data privacy challenges? Let’s find out.

Cookie syncing is a process used by AdTech platforms to exchange user data across different websites. Since cookies can only be read by the domain that created them, each domain has limited information about users and doesn’t have the full picture of their preferences and interests. To build that full picture and serve relevant ads to users, AdTech platforms—such as demand-side platforms (DSPs), supply-side platforms (SSPs), and data-management platforms (DMPs)—need access to user information from various domains.​

Cookie syncing works by matching the unique ID contained within each cookie across different websites. This enables all platforms to recognize common users and share or request the data. They can then segment and target audiences more easily. It’s ideal for programmatic advertising, which is all about showing the right ads to the right people at the right time.

The following image shows how single-partner cookie syncing works.

Here’s how cookie syncing works:

1. A user visits a website, which generates and stores a cookie in their browser or device.
2. The browser sends an ad request to an adtech partner—let’s say an SSP.
3. The SSP looks for a matching cookie in its directory. If it finds one, it uses that cookie’s data to target the user. If there’s no match, the SSP sends an ad request to another partner—let’s say the DSP.
4. The DSP then searches for a cookie to match the one placed by the website. Again, if it finds a match, it uses the cookie to display targeted ads.
5. What if neither the SSP nor the DSP have matching cookies? That’s when cookie syncing kicks in, with both platforms creating a new cookie for the user with a unique ID.
6. Every subsequent time the user goes online, both partners can gather extra data and update the cookies.

Let’s take a look at how cookie syncing can help you optimize ad campaigns.

Improves audience segmentation

Most advertisers segment their audiences to target different groups in different ways. You might segment by demographics such as location, age, gender, interests, or job title. How does each segment typically behave online? What keywords do they use?

If you only have cookie data from visitors to your own site, you would have to guess some of these attributes. But cookie syncing provides access to much more user data, allowing for more precise audience segmentation.

Boosts ad engagement 

When people see ads for products they are genuinely interested in—including those they have already browsed—they are more likely to engage.

By delivering a more relevant experience, you will improve click-through and conversion rates. You won’t waste money on users who are unlikely to convert, leading to a better ROI on your ad spend.

Facilitates cross-device tracking

Cookie syncing offers a deeper understanding of user behavior. By sharing data with ad partners, you’re not just analyzing demographics and browsing habits—you’re also tracking the devices users engage with.

Syncing helps identify when the same person logs in on different devices, just as it tracks visits across multiple websites. Cross-device tracking builds a more complete picture of user activity, ensuring they see relevant ads across all their devices.

Supports frequency capping 

Beyond helping you target the right users, cookie syncing also prevents over-targeting. While relevant ads boost engagement, seeing the same ad too often can drive users away. Plus, it’s inefficient to keep advertising to someone who has already converted.

With cookie syncing, you can recognize a single user across different platforms and limit ad exposure, ensuring you only target those who still need a nudge toward conversion.

Alongside the benefits for ad campaigns, there are some big challenges for cookie syncing.

Privacy concerns

Not everyone likes being tracked online. Some see it as an invasion of privacy, as cookies containing personal data can be shared among ad partners without user knowledge or consent.

There are also concerns about companies selling user data, and in some cases, bad actors could steal user information from a publisher’s platform. Without proper security measures, there’s a risk of data breaches or leaks.

Data inconsistencies

Different cookie policies across platforms can make it hard to collect and match data, leading to gaps in user information. If an advertising partner changes its cookie policies, it can disrupt the syncing process and create inconsistencies.

With data being shared across multiple platforms, it can also be difficult to track a single user—especially when they have multiple profiles. And when multiple companies use the same data for targeted ads, it reduces competitive advantage.

Browser restrictions

Due to privacy concerns, some tech companies have placed restrictions on cookie tracking. Apple and Mozilla, for example, have blocked third-party cookies in Safari and Firefox.

Google initially planned to phase out third-party cookies in Chrome but recently reconsidered. However, as privacy restrictions continue to grow, brands may need to find alternative ways to target users.

Strict data regulations

Many regions have laws governing data collection and user consent, such as the General Data Protection Regulation (GDPR) and the California Consumer Privacy Act (CCPA). More U.S. states are also introducing data privacy laws.

Non-compliance can lead to serious consequences, including legal action and hefty fines. For example, Ireland’s Data Protection Commission recently fined LinkedIn €310 million ($335 million) for unethical data processing in targeted ads.

Data privacy regulations have a significant impact on cookie syncing. Here’s how to navigate them:

Ensure user consent 

Businesses must comply with regulations like GDPR and CCPA, which require websites to obtain user consent before storing cookies—both essential and non-essential (e.g., tracking cookies).

It’s also crucial to maintain records of user consent to prove compliance if requested by legal authorities or users.

Use opt-in prompts

Make it easy for users to understand how their data will be used. Typically, this is done via a pop-up banner when they visit the site.

While many users may simply click “Accept” or “Reject” without reading the full policy, you must still publish it on your site, update it as needed, and allow users to withdraw consent at any time.

Collect only essential data

Most data regulations allow user data collection only if (a) you have consent and (b) it serves a specific purpose. By minimizing data collection, you reduce security risks.

You’ve likely seen options like “Accept all cookies” or “Essential cookies only.” Essential cookies ensure websites function properly, such as keeping items in a cart or remembering language preferences.

Enhance security measures to protect user data and build trust

​Users are more likely to trust you with their data—and consent to its use—if you demonstrate a commitment to security and ethical data practices. Ensure your cyber architecture includes robust security measures, such as SSL certificates, firewalls, and threat-scanning plugins. Additionally, implement a comprehensive backup and recovery plan.

Cookie syncing helps optimize programmatic ad campaigns by ensuring users see relevant, personalized ads. Targeting the right audience at the right time improves click-through rates, conversions, and ROI.

However, growing data privacy regulations pose challenges. Stay informed about restrictions, implement strong security protocols, and clearly communicate how you use user data.

What are cookies?

Cookies are small text files that store user information. When you visit a website, its server creates cookies and stores them on your device. If you return to the site, the cookies help it remember your previous interactions.

What’s the difference between first-party and third-party cookies?

First-party cookies are created by the website you visit, helping it remember user preferences. Third-party cookies are set by advertisers partnering with the website, enabling cross-site tracking and cookie syncing.

What are some alternatives to cookie syncing?

If you rely on first-party data to understand your audience, you can collect it through email marketing, surveys, and lead magnets. Another option is server-side tracking, where data is managed on your server instead of being stored in the user’s browser.

Author bio: Cynthia is a Senior Strategic Marketing Manager at Ardoq. She believes the wide-reaching benefits of Enterprise Architecture are often overlooked and underestimated—and she’s on a mission to change that.

Disclaimer: This article is for general informational purposes only and should not be taken as legal or professional advice. The views and opinions expressed in this article are solely those of the author and do not necessarily reflect the views of our organization. We do not endorse any products or services mentioned in the article.