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Cookie Syncing – What Is It & How Does It Work?

Programmatic video is the fastest-growing category of programmatic buying, but a lot of marketers are still struggling to get to grips with the basics.

And we can hardly blame them! Programmatic advertising is stuffed with more jargon than you can shake a stick at – that’s why Unruly is breaking down some of the most common terms.

This week it’s all about cookie syncing. So let’s start with some fundamentals…


What is cookie syncing?

To break it down: few people realize how dark of a place the internet would be without cookies. Cookies, also known as browser cookies or internet cookies, are pieces of data from a website that are stored on a user’s computer. Cookies allow us to add products to shopping carts, help us store passwords etc.


How does cookie syncing work?

Across various SSPs, demand partners bid around twice as often on impressions where they can apply audience targeting – and it’s cookie syncing that makes audience targeting possible.

Cookie syncing works by the SSP serving a tag (provided by the demand partner) on publisher pages, enabling the demand partner to associate an ID with the user. Next the demand partner passes its ID back to the SSP, who in turn stores the ID, ready to pass in the bid request next time we see the user. Kind of like a game of hot potato, if hot potato was played in the world of ad tech.

Because an auction needs to be resolved as quickly as possible to avoid missed revenue opportunities, there’s not enough time to conduct cookie syncing before we start the auction. This means there will always be some bid requests that go out without the demand partner’s user ID.

We initiate cookie syncing on every page impression for all of our demand partners. For a subset of our demand partners, they also initiate cookie syncing when they see users (e.g. when they serve ads on other exchanges). This reduces the instances of bid requests going out with demand partner user IDs.


What are the benefits of cookie syncing?

While cookie syncing looks like an all-round win (buyers can audience target and get better campaign KPIs; sellers can sell more supply and make more money!), as ever there are some challenges. Publishers often complain about the number of calls to third parties on their pages, citing the impact on the performance of their pages and also on behalf of users’ privacy concerns.