What is a supply-side platform (SSP)?
A supply-side platform is the technology publishers use to sell their ad space programmatically. It connects a website, app or streaming service to many buyers at once, runs the auction for each impression and applies the publisher's rules on price, ad quality and access. Its job is to get the publisher the best possible return on every impression.
The SSP is the sell-side counterpart of the demand-side platform that advertisers use to buy.
How an SSP works
Integration: the publisher connects the SSP through ad tags, a mobile SDK, a server-side connection or header bidding wrappers such as Prebid.
Bid request: when a user loads a page or app, the SSP packages information about the impression, such as the site, ad size, device and location, into a bid request.
Auction: the request goes out to connected DSPs, which respond with bids in milliseconds through real-time bidding. Most auctions today are first-price.
Rules: the SSP applies floor prices, blocked advertisers or categories, and deal priorities.
Result: the winning bid goes to the publisher's ad server, which decides the final ad to show.
Large publishers often work with several SSPs at once to increase competition for their inventory.
SSPs also handle the private side of selling. They package inventory into deals, generate deal IDs and publish sellers.json files that show which sellers they represent. Many SSPs also offer curation, where they bundle inventory and data into ready-made packages that buyers can activate with a single deal.
Why SSPs matter to advertisers
SSPs are publisher tools, but they shape what buyers can access and what they pay:
Supply access: the SSPs your DSP connects to determine which publishers and apps you can reach.
Fees: each SSP takes a share of the spend, so the same impression can cost more through one path than another.
Duplication: one impression may be offered by several SSPs at once, which can make you bid against yourself.
Quality: SSPs differ in how well they screen out invalid traffic and low-quality sites.
This is why many buyers practice supply path optimization, which means choosing the most direct and efficient SSP routes to each publisher.
SSP vs DSP
A DSP works for the buyer. It decides which impressions to bid on and how much to pay. An SSP works for the seller. It decides which bids to accept and at what minimum price. The two meet in the auction. An ad exchange is the marketplace where that auction happens, and today most SSPs run their own exchange, so the terms are often used together. Some ad tech companies run both a DSP and an SSP, but the two still serve opposite sides of the trade.
SSPs with AdGeeks
DV360, Amazon DSP and Adform each connect to a wide range of SSPs. AdGeeks traders review which supply paths deliver quality at a fair price, set up deals with publishers through their SSPs and shift budget away from routes that add cost without value.
