Bid.cat

Categories describing the creative, in the taxonomy named by Bid.cattax, or IAB Content Taxonomy 1.0 when that field is absent. Added in 2.3.

Currentstring arrayOptionalSince 2.3

Field facts

Exchanges check these against BidRequest.bcat or BidRequest.acat. Report the creative's real category even when that means the bid gets filtered.

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

{
  "seatbid": [
    {
      "bid": [
        {
          "cat": [
            "IAB2"
          ]
        }
      ]
    }
  ]
}

Leaving cat out when the request carries bcat, so the exchange has nothing to check.

Added in OpenRTB 2.3, 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
2.3 to 2.6-202606	string array	No	No

For a walkthrough of the whole object, read Bid response anatomy.