Glossary
What is Server-side bidding (S2S)?
Also called: S2S, server-to-server bidding, server-side header bidding
Server-side bidding runs the header bidding auction on a server: the page sends one request and the server calls each bidder, instead of the browser.
हिंदी में पढ़ेंWith client-side header bidding, Prebid.js runs the auction in the reader’s browser, and each bid adapter calls its SSP straight from the page. With server-side bidding, also called server-to-server or S2S, the page sends one request to a server such as Prebid Server, and the server calls the bidders. That lightens the load on the browser, and it is how apps, AMP pages and CTV bid.
The trade-off is identity. Bidders’ cookies live on their own domains, so a server cannot read them directly, and Prebid Server relies on cookie syncing to pass their reader IDs. Google’s Open Bidding is another server-side model: Ad Manager calls third-party exchanges server to server, and they compete with Ad Exchange in one auction, compared net of Google’s revenue share.
You do not have to pick one model. Prebid.js can send some bidders to Prebid Server and keep others in the browser, and the hb_source key-value lets you report client-side and server-side results side by side.
Example
A page runs 8 bidders. Client-side, the browser makes 8 bidder calls. Move 5 of them to Prebid Server and keep 3 in the browser, and the browser makes 3 bidder calls plus 1 call to the server: 4 requests instead of 8, half as many.
Why it matters to publishers
Fewer calls from the page can help speed, but bidders that cannot match their cookies may bid less. Comparing each bidder both ways, split by hb_source, shows which setup earns more.