Bid response

A bid response is the buyer's sealed envelope in a real-time bidding auction. After a DSP reads a bid request and decides the impression is worth buying, it answers within the auction's auction timeout with the bid price, the creative markup or a reference to it, the advertiser's domain, creative categories and, for deals, the Deal ID.

In OpenRTB, a response contains one or more "seatbids", each with bids for specific impressions. If the DSP does not want to bid, it returns an empty response (often an HTTP 204 "no content"). The exchange collects all responses, checks them against floors and publisher blocks, and chooses a winner. The winning bidder is then notified, typically through a "win notice" URL, and the price is settled.

Late responses are simply ignored, which is why latency matters. The advertiser domain and categories in the response let publishers block competitors or sensitive categories and help detect malvertising.

Think of it like this

A bid response is like a sealed tender returned to a contractor: the price, what you will deliver and who you are, handed in before the deadline or not at all.

An example

A DSP responds with a bid of US$2.35 CPM, a 300×250 HTML creative for a Singapore airline, and deal ID "SG-TRAVEL-Q3" within 85 milliseconds.