What is the optimizelyEndUserId cookie?
Stores a visitor's unique Optimizely identifier. It's a combination of a timestamp and random number. No other information about you or your visitors is stored inside.
Our October 2026 scan found it on 24 sites (1% of the 2,450 we scanned), set before any consent.
- Purpose
- Advertising
- Belongs to
- Optimizely
- Set as
- First-party (under the site's own domain)
- Typical lifetime
- 6 months (vendor says: 6 months) — about what the vendor documents
Sites that set optimizelyEndUserId before consent
The highest-ranked 24 of 24 sites.
- bbc.com4 tracking companies
- optimizely.com4 tracking companies
- prnewswire.com13 tracking companies
- jetbrains.com3 tracking companies
- sky.com5 tracking companies
- clevelandclinic.org7 tracking companies
- techtarget.com4 tracking companies
- asu.edu4 tracking companies
- elastic.co2 tracking companies
- scmp.com17 tracking companies
Show 14 more sites
- parallels.com4 tracking companies
- starbucks.com5 tracking companies
- heart.org5 tracking companies
- ctvnews.ca38 tracking companies
- unimelb.edu.au5 tracking companies
- docusign.com9 tracking companies
- hootsuite.com7 tracking companies
- smartsheet.com6 tracking companies
- united.com7 tracking companies
- bitly.com4 tracking companies
- premierleague.com7 tracking companies
- carnival.com3 tracking companies
- carfax.com1 tracking company
- westernunion.com5 tracking companies
Related cookies
Other cookies from Optimizely.
- optimizelySession20 sites
- optimizelyOptOut3 sites
How to stop it
Declining non-essential cookies in a site's consent banner should stop optimizelyEndUserId 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.