Bid Request

A bid request is a message sent from a supply-side platform (SSP) or ad exchange to a bidder — typically a component of a demand-side platform (DSP) — signalling that an ad impression is available for auction.

Each bid request carries contextual information about the placement (such as the page URL and content) as well as data about the user (for example, cookie data). The bidder evaluates this payload against an advertiser's campaign criteria — targeting parameters, audience segments, budget constraints — and decides whether to submit a bid on the impression or pass entirely.

Bid requests are the foundational unit of communication in real-time bidding (RTB), occurring in milliseconds as a page loads.