What is the criteo_write_test cookie?
criteo_write_test is an HTTP cookie set by Criteo, a company specialized in retargeting advertising (showing ads to visitors on other websites after they leave the original site). It usually appears as soon as the Criteo tracking script loads on a page, either directly on the visited site or through an advertising partner using Criteo's services.
Its stated purpose is purely technical: it checks whether the domain in question is able to set cookies in the user's browser, before Criteo's other cookies (used for actual ad tracking and personalization) are placed.
What data it stores
It does not store directly identifiable personal data; the value is typically minimal or empty, used only to confirm the browser's ability to accept cookies from the Criteo domain. The exact value format may vary and is not publicly documented in detail.
The result of this test (success or failure) is sent back to Criteo's servers as part of their advertising infrastructure.
What it is used for
For Criteo, this cookie helps validate the browser environment before enabling retargeting and ad-measurement mechanisms. If the test fails (for example, the browser blocks third-party cookies), Criteo may adjust how it attempts to track the visitor.
For the website operator, the presence of this cookie indicates that a Criteo advertising/retargeting script is running on the page, either integrated directly or through a partner.
Does it require consent?
Although it plays a technical testing role, criteo_write_test is part of Criteo's marketing/advertising cookie chain and is classified accordingly. Under GDPR and the ePrivacy Directive (implemented in Romania via Law 506/2004), marketing cookies require the visitor's prior, explicit, informed consent.
- The site operator must disclose this cookie in the cookie policy, listing the provider (Criteo) and category (marketing).
- The Criteo script must not load before the visitor gives consent for the marketing category.
- Consent must be as easy to withdraw as it was to give.
How to block or delete criteo_write_test
A visitor can delete or block this cookie via browser settings (managing cookies per site or blocking third-party cookies), as well as through dedicated privacy extensions.
For website operators, the correct approach isn't manual deletion but preventing the Criteo script from loading before consent. A CMP platform like CookieFix can automatically block the Criteo script until the visitor accepts the marketing category, preventing the cookie from being set prematurely.
Frequently asked questions
It's a technical cookie used by Criteo to check whether the browser can receive cookies, before Criteo's actual advertising tracking cookies are placed.
Yes, since it's part of Criteo's marketing/advertising infrastructure, prior visitor consent is required under GDPR and applicable ePrivacy laws.
It has a very short lifespan, roughly one minute, since it's only used for the initial technical test.
The website should be configured so the Criteo script only loads after the visitor accepts marketing cookies, for example through automatic blocking provided by a CMP.