What is a DSP (demand-side platform)?

What a DSP does

A DSP is the buyer's side of programmatic. It connects to exchanges, receives bid requests, decides which are worth bidding on and at what price, and manages the campaign that results.

Its job is compression: without one, an advertiser would need a relationship, an integration and a bidding capability for every exchange. The DSP makes them one account with one set of campaigns and one report.

What it actually decides

• Eligibility. Does this impression match any active campaign's targeting and exclusions.
• Valuation. What is it worth, based on predicted outcome — usually a model, sometimes a rule.
• Pacing. Spending the budget evenly rather than exhausting it by lunchtime.
• Frequency. Not over-serving the same user.
• Creative selection, where several are eligible.

Fees and where the money goes

A DSP typically takes a percentage of media spend, and it is one of several layers doing so. Between the advertiser's budget and the publisher's revenue sit the DSP, the exchange, the SSP, and frequently data and verification vendors.

Two things are worth knowing about this. The DSP fee is usually the most visible and rarely the largest. And a DSP that also owns supply-side assets has an incentive that is worth understanding before assuming neutrality in how it routes spend.

How an AI DSP differs

An AI DSP performs the same role against a different signal. A conventional DSP asks how valuable this user is; an AI DSP asks how valuable this moment is, because there is no durable identity to value and there is a stated intent to read instead.

The engineering constraint is also harder — the decision must complete inside the assistant's response generation rather than during page load. That is why AI buying generally runs on platforms built for the surface rather than as a module in an existing DSP.