What is the _clsk cookie?
This cookie is installed by Microsoft Clarity to store information of how visitors use a website and help in creating an analytics report of how the website is doing. The data collected including the number visitors, the source where they have come from, and the pages visited in an anonymous form.
Our October 2026 scan found it on 5 sites (0% of the 2,450 we scanned), set before any consent.
- Purpose
- Analytics
- Belongs to
- Microsoft
- Set as
- First-party (under the site's own domain)
- Typical lifetime
- 1 day (vendor says: session)
Sites that set _clsk before consent
The highest-ranked 5 of 5 sites.
- tailscale.com7 tracking companies
- cmu.edu6 tracking companies
- ssl.com9 tracking companies
- guard.io14 tracking companies
- coxautoinc.com10 tracking companies
Related cookies
Other cookies from Microsoft.
- MUID38 sites
- ASP.NET_SessionId23 sites
- _uetsid22 sites
- _uetvid21 sites
- MR16 sites
How to stop it
Declining non-essential cookies in a site's consent banner should stop _clsk being set on later visits. Blocking third-party cookies in your browser settings stops the third-party kind everywhere, and clearing cookies for a site removes any it already set.
Description from the Open Cookie Database (Apache 2.0).
Understanding this page
- How cookie lifetimes work, and why a 13-month _ga matters
What a cookie's "expires" field actually controls, why Google Analytics ships a 2-year default that many sites cut down to 13 months, and how Safari's 7-day cap on script-set cookies changes the picture.
- First-party vs third-party cookies (and why "first-party" still tracks you)
What the distinction actually means technically, why browsers only block one of the two, and how CNAME cloaking, server-side tagging and cookies like _ga let sites keep tracking under their own domain.
- How to block or limit trackers
Browser privacy settings, content blockers, Global Privacy Control and clearing cookies compared honestly — what each one actually stops, what it doesn't, and what it costs you in return.