User.buyeruid

The buyer's own ID for this user, which the exchange looks up in its match table and inserts separately for each bidder. Unless the two parties agreed otherwise, it comes from a cookie sync.

CurrentstringOptionalSince 2.0

Field facts

Path: user.buyeruid
Object: User
Type: string
Requirement: Optional
Added: OpenRTB 2.0
Spec section: 3.2.20

How it is used

A DSP can act on this ID directly for frequency capping and audience targeting because it is the DSP's own. It exists only after a sync, so coverage drops on browsers that block third-party cookies, and it is usually absent in apps, where device.ifa and user.eids carry identity. Through 2.5 the spec recommended sending at least one of id or buyeruid; 2.6 drops that label. The 2.3 table misspelled the name as buyerid, and 2.3.1 fixed it.

Example

Where the field sits in a payload, with everything else left out:

{
  "id": "req-1",
  "user": {
    "buyeruid": "dsp-uid-0000-example-1234"
  }
}

Common mistakes

Sending the same buyeruid to every bidder. The value belongs to one buyer and means nothing to the others.
Putting the exchange's own cookie ID here. That belongs in user.id.

Version history

Added in OpenRTB 2.0, and present in the latest snapshot. The table shows how each version's spec text types the field.

Versions	Type in the spec	Required	Deprecated
2.0 to 2.2	string	No	No
2.3.1	string	Recommended	No
2.4	string	Recommended	No
2.5	string	Recommended	No
2.6-202210 to 2.6-202606	string	No	No

Versioned rules that name this field

openrtb.2.3.1.user.buyeruid OpenRTB 2.3.1 corrected the buyer-specific user ID attribute spelling to buyeruid.

Related fields

Other User fields

For a walkthrough of the whole object, read User identity and EIDs.