The _uetsid cookie
The Microsoft Advertising UET session cookie, holding the session ID for a single visit to the site.
_uetsid at a glance
- Cookie name
_uetsid- Vendor
- Microsoft UET
- Category
- Advertising
- Party
- First-party
- Lifetime (observed)
- 1 dayObserved median across TagPipes scans. The vendor does not document a lifetime, so this is not its configured value.
- Set on
.<your-domain>- Value format
- Session ID followed by extra parameters (exact encoding not documented by vendor)
- Name match
- Exactly
_uetsid
What the _uetsid cookie does
The Microsoft Advertising Universal Event Tracking (UET) tag stores the session ID for a visit in _uetsid, on the site's own domain. Since July 2023 it also carries extra parameters used by UET's website insights, including an insights session ID, a timestamp, a page number and upload flags.
Microsoft documents the purpose and contents but not the lifetime. 1 day is the commonly reported figure and matches the median TagPipes observed. It's usually found alongside _uetvid.
What TagPipes observed
0.70%
of sites scanned set it (288 of 41,162)
1 day
median observed lifetime
TagPipes scanned 41,162 public websites between August 11, 2026 and September 13, 2026, loading up to three pages per site in a real browser as a first-time visitor. _uetsid was present on 288 of them.
It was set as a first-party cookie on 256 sites and as a third-party cookie on 32. A site can count in both. Where it was stored as a persistent cookie, the median lifetime we recorded was 1 day.
Often found alongside
Percentage of sites with _uetsid where the other cookie was also present.
Technologies detected on the same sites
- Google Analytics on 99% of them (55% of all sites scanned)
- Microsoft UET on 99% of them (0.99% of all sites scanned)
- Google Ads on 94% of them (12% of all sites scanned)
- DoubleClick on 92% of them (11% of all sites scanned)
- Google Tag Manager on 85% of them (30% of all sites scanned)
Aggregate figures across all sites scanned. Websites of TagPipes customers are excluded, no individual site is named, and cookie values are never read or stored. Snapshot dated September 13, 2026.
How to check for _uetsid on a website
- Open the site in Chrome, then open DevTools (F12, or Cmd+Option+I on a Mac).
- Go to the Application tab and expand Cookies in the left panel.
- Select each domain listed there and look for
_uetsid. The Expires column shows when it will be deleted. - If it is not there, reload the page. Many cookies are only set after a tag has loaded, and some only after a visitor has made a consent choice.
Other Microsoft UET cookies
Sources
- Microsoft Advertising Help: UET frequently asked questions
- Microsoft Advertising Help: UET and consent FAQ
Purpose and value format checked against the vendor documentation above on . The observed lifetime and the figures under What TagPipes observed are TagPipes scan data from September 13, 2026, not values documented by the vendor. Vendors change their cookies, and sites can configure their own names and lifetimes. Browse all cookies.
Know every cookie your own site sets
TagPipes Pulse identifies the cookies dropped on your site and flags unclassified or miscategorized ones. Shield builds your cookie declaration from a real scan rather than a questionnaire.
TagPipes monitors, configures and reports. It does not determine legal compliance and does not provide legal advice. Output is informational and reflects observed state at the time of observation. Rawsoft's expertise is technology, not law; please confirm any regulatory interpretation with your own counsel.