What is the PREF cookie?
PREF is an HTTP cookie set by YouTube, a service owned by Google, when a user visits youtube.com or interacts with an embedded YouTube video player on another website. It commonly appears on sites that display YouTube clips, even if the visitor has no Google account.
The cookie is set on the .youtube.com domain, meaning it is shared across YouTube subdomains and may also be relayed to other Google services when the player is embedded.
What data it stores
PREF stores preferences related to how a user interacts with the YouTube player, such as interface language, preferred video quality, or other display settings. The exact value format is not publicly documented and may change over time as Google updates the service.
This data is sent to Google/YouTube servers whenever the visitor interacts with the player or loads a YouTube page.
What it is used for
The stated purpose is functional: the cookie lets YouTube remember a user's playback preferences across sessions, so the player behaves consistently (for example, keeping the same video quality or language) without requiring the user to reset settings each time.
For site owners who embed YouTube videos, this cookie is part of the player's normal operation, but it also feeds into the broader viewing profile Google builds about users across the web.
Does it require consent?
CookieFix classifies PREF under preferences (functional). Although it relates to feature personalization, the cookie is set by a third party (Google) and may contribute to user profiling, so under ePrivacy and GDPR it should generally be treated as requiring prior visitor consent rather than as strictly necessary.
Site owners must list it explicitly in their cookie policy, categorize it correctly in the consent banner, and make sure the YouTube player does not load by default before consent is obtained, if the site targets users in Romania/the EU.
How to block or delete PREF
A visitor can delete or block PREF through browser settings (Chrome, Firefox, Edge, etc., under per-site cookie management), or use YouTube's privacy-enhanced mode via the youtube-nocookie.com domain for embeds.
For site owners, the correct approach is to automatically block the YouTube player script until consent is given. A CMP like CookieFix can do this automatically, preventing the YouTube embed (and the PREF cookie along with it) from loading until the visitor accepts the preferences category.
Frequently asked questions
It is not considered high-risk, but it does contribute to Google's profiling of a user's viewing behavior, which is why it requires consent.
It also appears on third-party sites that embed YouTube videos, since the embedded player sets the cookie from the .youtube.com domain.
Yes, as a third-party cookie used for personalization, it should be treated as requiring prior consent under ePrivacy and GDPR.
You can use the youtube-nocookie.com domain for embeds, or block the player from loading until consent is given via a CMP.