Google’s Turtledove: Retargeting after the 3P cookie’s death

A user on r/adops recently posed the question:

If we turned off 3p cookies tomorrow – would retargeting be impossible or done in a different but equally effective way?

Excellent question, and Turtledove is the answer.

Google’s Turtledove proposes an entirely new method to serve ads. The proposal is the core, foundational infrastructure for rebuilding how most programmatic ads are bought and sold. Turtledove only supports retargeting and contextual targeting, but does so in a way that purposefully retains user privacy. The impact of the proposal implies massive change in the marketplace because it changes how the auction itself functions, and acts as a stepping stone for other proposals to add features to.

We are acutely aware that [Turtledove] represents a substantial change from how the ad ecosystem works today…

Michael Kleber, Google

How is retargeting affected by the death of the third party cookie?

Retargeting will not work without the 3P cookie, unless we implement new solutions like Turtledove or a universal ID. Retargeting uses first party data, but that is done via third party cookies. The details of this deserve their own write-up, and Clearcode wrote a good one. The image below is also Clearcode’s.

How is contextual targeting affected?

From a technical perspective, contextual targeting can function without the third party cookie. Google still wants to address contextual though because fingerprinting and other major privacy concerns operate with the help of contextual. Google explicitly calls out the mixing of contextual and third party data as a privacy concern.


Two Uncorrelated Requests Then Locally-Executed Decision on Victory

Turtledove replaces core functions of programmatic adserving, namely data collection, storage, and auction mechanics. These are very complicated topics, so I’ve kept this post nontechnical. Technical details about what the API could look like can be found on github.


Google’s proposal implements three major changes:

  1. User data (Steve visited is stored in the user’s browser and is not accessible to anyone else. Currently, that data is stored and owned by many different companies and is freely sold in the market.
  2. The ad auction occurs in the browser. Data from the auction only exists in and cannot leave the browser. Currently, the auction occurs in an ad network’s server, and most data about the website/user/etc is available to all parties (publisher, advertiser, ad networks, etc).
  3. Two ad requests are made prior to the auction. One for audience data and an entirely separate request for contextual. Currently, an open ad slot has one request made that includes any and all data available (context, user, etc)


In the Turtledove world advertisers and agencies running retargeting campaigns will operate largely how they do know. An advertiser can track users on their site, place them in audience pools, and target them later on other websites. The change here is purely technical – there are no pixels or cookies. We’ve just changed how users are tracked and where that data is stored (in the user’s browser, rather than with your Adtech Vendor/DSP/DMP/etc).

Auction Changes

The mechanics of the auction operate differently, but a DSP will operate in the same way as now. Currently you don’t have much visibility into the auction, and that will not change. DSPs and vendors lose a lot of data about the auction itself, but that hasn’t been explored yet.

Changes Affecting Advertisers

The drastic change is in the two uncorrelated requests piece. Currently, an advertiser can mix contextual data and any other data in their DSP. This enables brand safety, page quality, and targeting strategies like High Income Users Reading About Sports. With Turtledove this is no longer possible. Turtledove explicitly separates contextual and other data for privacy reasons. 

When advertising you are now forced to choose to target data about the user (retargeting, etc) or target websites (contextual). Advertiser’s also can’t see what websites their ads have served on. Advertiser’s lose the ability to mix these as historically advertisers, publishers, and vendors have used this mixing to track users in unethical ways. 


The list below makes it seem like this is a minor change. But Turtledove only tries to enable two capabilities (retargeting and contextual). Turtledove entirely relies on other proposals to implement things like third party audiences, brand safety, measurement, viewability, etc.

  • Retargeting works like normal
  • Contextual works like normal
  • Advertisers can’t mix contextual and data targeting. For non-contextual targeting that means:
    • No brand safety
    • No viewability/etc
    • No visibility into what website your ads served on
    • Whitelists and blacklists severely handicapped

The proposal accomplishes two of the W3C’s stated goals – namely ethical data collection, and retaining the interests of browsers. Though still early on, it doesn’t provide much functionality for advertisers or publishers. Turtledove is truly just the groundwork for additional proposals and I’d expect its functionality to change significantly. That being said, Turtledove has existed largely unchanged for about 8 months, and we’re only 18 months away from the supposed date it needs to function by.

As of August 2020 I have not seen any other proposals for rebuilding the ecosystem, at least that the W3C has considered. All other proposals build on Turtledove or solve for other problems. It seems there is significant opportunity here.

Update: Per this github issue “Contextual” also includes audiences the publisher owns, though its never discussed how those would be made available to advertisers.

Leave a Reply

Your email address will not be published. Required fields are marked *