What is the _clsk cookie?
_clsk is an HTTP cookie set by the Microsoft Clarity script, Microsoft's free behavioral analytics tool for heatmaps and session recordings. It appears on a website as soon as the Clarity tracking code loads and runs, whether on a blog, an online store, or a company website.
The cookie is set by the domain of the visited site (first-party from the visitor's perspective), but the collected data is sent to Microsoft Clarity's servers for processing and display in the analytics dashboard.
What data it stores
_clsk stores an identifier that ties a visitor's activity (clicks, mouse movements, scrolling) to a single browsing session on the site, allowing Clarity to reconstruct the session as a recording or heatmap. The exact value is a string generated by the Clarity script and generally does not contain directly identifying data such as a name or email address.
The session data is transmitted to Microsoft Clarity's infrastructure, where it is aggregated into user behavior reports.
What it is used for
For site owners, _clsk makes it possible to see how visitors actually navigate: where they click, how far they scroll, and where they run into friction — useful information for improving design and conversions. For Microsoft, the cookie supports the operation of the Clarity service, offered free of charge as part of the Microsoft Advertising ecosystem.
It has no role in displaying content or in the technical functioning of the site — its purpose is purely analytical.
Does it require consent?
_clsk is classified as a statistics (analytics) cookie, since it tracks visitor behavior throughout a session. Under GDPR and the ePrivacy Directive (implemented in Romania via Law 506/2004), this type of cookie requires prior consent from the visitor before being set, except in very limited cases where it could be considered strictly necessary (rarely applicable to Clarity).
- The site owner must list the _clsk cookie in the cookie policy, under the statistics category.
- The Clarity script must be blocked until consent is given.
- Refusing consent must not affect the site's basic functionality.
How to block or delete _clsk
A visitor can delete or block _clsk at any time from browser settings (Chrome, Firefox, Edge, Safari), in the cookie and site data management section, or by using private/incognito browsing to prevent it from being stored.
For site owners, the correct approach is to prevent the Microsoft Clarity script from running at all before consent is given. A CMP such as CookieFix can automatically block the Clarity script until the visitor accepts the statistics category, preventing the _clsk cookie from being set prematurely.
Frequently asked questions
No, it's a standard analytics cookie that doesn't contain sensitive data like passwords or financial information; its purpose is to help understand browsing behavior.
It typically lasts one day, designed to cover a single browsing session of the visitor on the site.
Yes, any site using Microsoft Clarity should mention _clsk in its cookie policy, under the statistics category.
Clarity relies on cookies such as _clsk to link interactions to a session, so the service's full functionality depends on this cookie and on visitor consent.