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Cookie reference · Microsoft UET

The MUID cookie

Microsoft's cross-service browser ID, a GUID read by Microsoft Advertising UET, Clarity and Bing.

MUID at a glance

Cookie name
MUID
Vendor
Microsoft UET
Category
Advertising
Party
Third-party
Typical duration
13 months
Set on
.bing.com, .clarity.ms and other Microsoft domains
Value format
GUID (32 hexadecimal characters)
Name match
Exactly MUID

What the MUID cookie does

MUID stores a GUID that identifies a unique web browser across Microsoft sites and services. Microsoft uses it for advertising, site analytics and operational purposes, and related cookies refresh it and sync it across Microsoft domains. Both the Microsoft Advertising UET tag and Microsoft Clarity read it when their scripts load.

It's set on Microsoft's own domains, so on your site it appears as a third-party cookie. The 13 month lifetime comes from Microsoft's UET FAQ, which describes the Microsoft cookie containing a GUID without naming MUID on that line.

What TagPipes observed

1.8%

of sites scanned set it (746 of 41,162)

390 days

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. MUID was present on 746 of them.

It was set as a first-party cookie on 0 sites and as a third-party cookie on 746. A site can count in both. Where it was stored as a persistent cookie, the median lifetime we recorded was 390 days.

Often found alongside

Percentage of sites with MUID where the other cookie was also present.

Technologies detected on the same sites

  • Google Analytics on 97% of them (55% of all sites scanned)
  • Google Tag Manager on 77% of them (30% of all sites scanned)
  • Google Fonts on 76% of them (78% of all sites scanned)
  • Microsoft Clarity on 68% of them (1.4% of all sites scanned)
  • Google Ads on 66% of them (12% 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 MUID on a website

  1. Open the site in Chrome, then open DevTools (F12, or Cmd+Option+I on a Mac).
  2. Go to the Application tab and expand Cookies in the left panel.
  3. Select each domain listed there and look for MUID. The Expires column shows when it will be deleted.
  4. 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

Purpose, duration and value format checked against the vendor documentation above on . 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.

See Pulse See Shield

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.