Definition
A bid request is the packet of information an ad exchange sends to potential buyers when an impression becomes available in a real-time auction. It describes the opportunity: the site or app and the specific placement, the ad format and dimensions, the device, operating system and connection, coarse or precise location, and whatever user signals are permitted — an advertising identifier or a privacy-preserving token, contextual signals about the page, and sometimes first-party audience data attached by the publisher.
Buyers' systems read this in a few milliseconds and decide whether, and how much, to bid.
The bid request is where targeting actually happens in programmatic. Everything a buyer knows about an impression before deciding to pay for it is in that packet, so its richness — and its accuracy — determines how well a campaign can be targeted and how much waste there is.
In context
Privacy changes have reshaped what a bid request can contain. The deprecation of third-party cookies and mobile-identifier restrictions (App Tracking Transparency) have reduced the availability of stable user identifiers, so bid requests increasingly rely on contextual signals, publisher first-party data, and privacy-preserving identity frameworks.
For iGaming, this means programmatic targeting in the open exchange is coarser than it was, and audience-based strategies lean more on the operator's own first-party data activated through the DSP.
Bid-request quality is also an anti-fraud and brand-safety concern. Spoofed requests misrepresent the site or app to attract higher bids; requests from made-for-advertising sites describe low-value inventory dressed up as premium; and inconsistencies between claimed and actual attributes are a fraud signal.
Buyers and verification vendors inspect bid requests for these tells, use ads.txt/app-ads.txt and sellers.json to confirm the seller is authorised, and prefer supply paths where the bid request can be trusted. For an operator, treating the bid request as data to be verified rather than accepted at face value is part of running programmatic without funding fraud.
Worked example
An operator's verification vendor flags that a batch of bid requests claiming to be from a premium news app do not match the app's registered ads.txt seller and have implausibly uniform user attributes. The DSP blocks that supply source, and measured invalid-traffic rate on the campaign drops from 9% to under 2%.
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