EID.mm

How the ID was matched to this request, as an integer from the AdCOM ID Match Methods list: 0 unknown, 1 no match (the ID came directly from a cookie or device ID), 2 browser cookie sync, 3 authenticated, 4 observed, 5 inference.

CurrentintOptionalSince 2.6-202409

Field facts

Path: user.eids.mm
Object: EID
Type: int
Requirement: Optional
Added: OpenRTB 2.6-202409
Values: AdCOM list ID Match Methods
Spec section: 3.2.27

How it is used

Added in OpenRTB 2.6-202409. Values 500 and above are vendor-specific. Buyers use it to weigh match quality: an authenticated match from a login or hashed email is generally stronger than an inference from IP address and user agent.

Allowed values

Value	Meaning
`0`	Unknown: The match method is not known or not reported.
`1`	No Match: No matching took place: the ID came straight from a third-party cookie or the device's resettable advertising ID.
`2`	Browser Cookie Sync: The ID was matched through a real-time browser cookie sync between two platforms.
`3`	Authenticated: The match was based on user authentication, such as an email login or hashed personal data.
`4`	Observed: The match came from a first-party observation without authentication, such as a first-party cookie or local storage ID.
`5`	Inference: The match was inferred from signals such as IP address and user agent across browsers or devices, without authentication.
`500+`	Vendor-specific: Match methods defined by an ID provider or exchange and agreed with buyers outside the specification.

Example

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

{
  "id": "req-1",
  "user": {
    "eids": [
      {
        "mm": 3
      }
    ]
  }
}

Common mistakes

Sending 3 (authenticated) for IDs linked by IP address and user agent. That is inference, value 5, and misstating it misleads every buyer that prices on match quality.
Sending it as a string.

Version history

Added in OpenRTB 2.6-202409, 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
2.6-202409	Listed in this release's notes; IAB's tagged spec file for it does not include the field yet.
2.6-202501 to 2.6-202606	int	No	No

Related fields

Other EID fields

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