What is DSP (demand-side platform)?

A DSP works for the buyer. Advertisers or their agencies load budgets and campaigns into it. When a bid request arrives from an SSP or exchange, the DSP checks it against those campaigns and decides whether the impression is worth buying and how much to bid, all within the deadline set in the request.

A DSP can only price what the request tells it. The page, ad size, device, country, consent signals and the supply chain object all feed its decision. Users it can recognise usually attract higher bids, because buyers can target them, limit repeats and measure results.

In first-price auctions, DSPs use bid shading, bidding below their true value based on what usually wins. Many DSPs also score the different paths that reach the same impression and keep only the best ones, checking ads.txt, sellers.json, the supply chain object and fees. A path that fails those checks can lose that buyer’s spend.