What is the d cookie?
The „d” cookie is part of Quantcast's audience measurement and advertising system. Quantcast is an ad-tech and web analytics company. The cookie is set by Quantcast scripts (such as Quantcast Measure or components of the Quantcast advertising platform) when they run on a website.
It typically appears on a visitor's first visit to a site using Quantcast services for audience statistics, audience segmentation, or real-time bidding. It is served from the .quantserve.com domain, so it functions as a third-party cookie.
What data it stores
The cookie stores an identifier associated with the visitor's browser, used to recognize it on later visits to sites that use Quantcast. The exact value format is not publicly documented in detail and may vary; it typically does not contain directly identifiable data such as a name or email address.
Information collected via this identifier is sent to Quantcast's servers (.quantserve.com) and may be combined with data from other partner sites to build aggregated audience profiles or advertising segments.
What it is used for
For Quantcast, the „d” cookie is used for audience measurement (how many unique visitors a site gets, from which demographic categories) and for building audience segments used in programmatic ad auctions.
For the site owner, this cookie provides access to traffic statistics supplied by Quantcast and, if the site monetizes ad space through the Quantcast platform, it helps deliver more relevant targeted ads to visitors.
Does it require consent?
Under CookieFix's classification, the „d” cookie falls into the marketing/advertising category, since it is used for cross-site tracking and targeted advertising. It is not strictly necessary for the site to function.
- Requires prior visitor consent under the GDPR (Regulation 2016/679) and the ePrivacy Directive as implemented locally (in Romania, Law 506/2004).
- Site owners must disclose it in their cookie policy, listing the provider, purpose, and duration.
- The script that sets this cookie should not load before the visitor selects the „marketing” category in the consent banner.
How to block or delete d
A visitor can manually delete or block the „d” cookie from browser settings (Chrome, Firefox, Edge, Safari – cookie management for specific sites or for the quantserve.com domain), or use cross-site tracking protection features available in modern browsers.
For site owners, the correct approach isn't manual deletion but preventing the cookie from being set before consent. A consent management platform like CookieFix can automatically block Quantcast scripts until the visitor explicitly accepts the marketing category, avoiding unauthorized placement of the cookie.
Frequently asked questions
It's not malicious; it's used for audience measurement and targeted advertising. It can be considered intrusive due to cross-site tracking, which is why it requires consent.
The typically reported duration is around 3 months, after which it expires automatically unless renewed on a later visit.
Yes. As a marketing/tracking cookie, explicit consent must be obtained before it is set, under GDPR and ePrivacy-based legislation.
You can inspect cookies in browser DevTools (Application/Storage tab) or run a cookie scanner that automatically detects active Quantcast scripts on your site.